Trichloroethylene cancer epidemiology: a consideration of select issues

The Impact of Environmental Health Determinants in Surgical Oncology

Environmental determinants of health refer to external factors in our surroundings that influence health outcomes. It is estimated that healthier environments could prevent almost one-quarter of the global burden of disease. Additionally, environmental factors, including lifestyle factors, air pollution, chemical exposures, and natural exposures, are responsible for a significant incidence of cancers and premature cancer deaths. Minority populations, low-income populations, children, and older adults are at increased risk for oncologic risks secondary to environmental factors.

Occupational exposures and cancer risk in commercial laundry and dry cleaning industries: a scoping review

BACKGROUND

The laundry and dry cleaning industries are critical for maintaining cleanliness and hygiene in our daily lives. However, they have also been identified as sources of hazardous chemical exposure for workers, leading to potentially severe health implications. Despite mounting evidence that solvents like perchloroethylene and trichloroethylene are carcinogenic, they remain commonly used in the industry. Additionally, while alternative solvents are increasingly being utilized in response to indications of adverse health and environmental effects, there remains a significant gap in our understanding of the potential risks associated with exposure to these new agents.

METHODS

This study aims to identify gaps in the literature concerning worker exposure to contemporary toxic chemicals in the laundry and dry cleaning industry and their associated carcinogenic risks. A scoping review of peer-reviewed publications from 2012 to 2022 was conducted to achieve this objective, focusing on studies that detailed chemical exposures, sampling methods, and workers within the laundry and dry cleaning sector.

RESULTS

In this scoping review, 12 relevant papers were assessed. A majority (66%) examined perchloroethylene exposure, with one notable finding revealing that biomarkers from dry cleaners had significant micronuclei frequency and DNA damage, even when exposed to PCE at levels below occupational exposure limits. Similarly, another study supported these results, finding an increase in early DNA damage among exposed workers. Separate studies on TCE and benzene presented varied exposure levels and health risks, raising concern due to their IARC Group 1 carcinogen classification. Information on alternative solvents was limited, highlighting gaps in health outcome data, exposure guidelines, and carcinogenic classifications.

CONCLUSION

Research on health outcomes, specifically carcinogenicity from solvent exposure in dry cleaning, is limited, with 66% of studies not monitoring health implications, particularly for emerging solvents. Further, findings indicated potential DNA damage from perchloroethylene, even below set occupational limits, emphasizing the need to reevaluate safety limits. As alternative solvents like butylal and high-flashpoint hydrocarbons become more prevalent, investigations into the effects of their exposure are necessary to safeguard workers' health. This scoping review is registered with the Open Science Framework, registration DOI: https://doi.org/10.17605/OSF.IO/Q8FR3 .

Detection Rate and Spectrum of Pathogenic Variations in a Cohort of 83 Patients with Suspected Hereditary Risk of Kidney Cancer

Hereditary predisposition to cancer affects about 3-5% of renal cancers. Testing criteria have been proposed in France for genetic testing of non-syndromic renal cancer. Our study explores the detection rates associated with our testing criteria. Using a comprehensive gene panel including 8 genes related to renal cancer and 50 genes related to hereditary predisposition to other cancers, we evaluated the detection rate of pathogenic variants in a cohort of 83 patients with suspected renal cancer predisposition. The detection rate was 7.2% for the renal cancer genes, which was 2.41-fold higher than the estimated 3% proportion of unselected kidney cases with inherited risk. Pathogenic variants in renal cancer genes were observed in 44.5% of syndromic cases, and in 2.7% of non-syndromic cases. Incidental findings were observed in CHEK2, MSH2, MUTYH and WRN. CHEK2 was associated with renal cancer (OR at 7.14; 95% CI 1.74-29.6; p < 0.003) in our study in comparison to the gnomAD control population. The detection rate in renal cancer genes was low in non-syndromic cases. Additional causal mechanisms are probably involved, and further research is required to find them. A study of the management of renal cancer risk for CHEK2 pathogenic variant carriers is needed.

Occupational Exposures in Commercial Laundry and Dry Cleaning Industries and their Associative Cancers: A Scoping Review

Background

The laundry and dry cleaning industries are critical for maintaining cleanliness and hygiene in our daily lives. However, these industries have also been identified as sources of hazardous chemical exposure for workers, leading to potentially severe health implications. Despite mounting evidence that solvents like perchloroethylene and trichloroethylene are carcinogenic to humans, they remain the most commonly used solvents in the industry. In addition, while alternative solvents are increasingly being utilized in response to evidence of adverse health and environmental effects, there remains a significant gap in our understanding of the potential risks associated with exposure to these new agents.

Methods

A systematic scoping review was conducted to identify prevalent toxic substances in the commercial laundry and dry cleaning industries that workers are exposed to and, further, to identify gaps in the existing literature regarding those exposures and related cancer development. Reported study exposure values were compared with current occupational exposure limits and biological exposure indices.

Results

Most studies examined perchloroethylene exposure in the dry cleaning industry, with one notable finding being that genotoxic effects were found even below current occupational exposure limits. Separate studies on TCE and benzene presented varied exposure levels and health risks, raising concern due to their IARC Group 1 carcinogen classification. Lastly, data on alternative solvents was limited, with a lack of health outcome data and gaps in their exposure guidelines and carcinogenic classifications.

Conclusion

A gap in research exists regarding health outcomes, particularly cancer development, from solvent exposure in the dry cleaning industry. Most studies (66%) overlooked health implications, especially for emerging solvents. Further, results showed potential DNA damage from the established solvent, perchloroethylene, even below current occupational exposure limits, emphasizing the need to reevaluate safety limits. As alternative solvents like butylal and high-flashpoint hydrocarbons become more prevalent, investigations into the effects of their exposure are necessary to safeguard workers' health. This scoping review is registered with the Open Science Framework, registration DOI: https://doi.org/10.17605/OSF.IO/Q8FR3.

The global, regional, and national burden of kidney cancer and attributable risk factor analysis from 1990 to 2017

BACKGROUND

Kidney cancer's incidence and mortality vary in different regions and countries. To compare and interpret kidney cancer's burden and change trends in the globe and in different countries, we conducted this study to report the global kidney cancer burden and attributable risk factors.

METHODS

Data about kidney cancer's incidence, death, disability-adjusted life-year (DALY) were extracted from the Global Burden of Diseases 2017. Besides, social-demographic index (SDI) values were adopted to investigate the correlation between kidney cancer's burden and social development degrees.

RESULTS

In the globe, the incidence case of kidney cancer increased sharply from 207.31*103 in 1990 to 393.04*103 in 2017. High SDI countries had the highest kidney cancer's burden with a decreased trend in incidence rate. On the contrary, the incidence rate was rapidly increased in low-middle SDI countries, although their burden of kidney cancer kept relatively low. At the same time, the deaths of kidney cancer increased from 68.14*103 to 138.53*103, and the kidney cancer-related DALYs increased from 1915.49*103 in 1990 to 3284.32*103 in 2017. Then, we searched the GBD database for kidney cancer-related risk factor. The high body-mass index and smoking were the main factors contributing to kidney cancer-related mortality.

CONCLUSIONS

Generally, from 1990 to 2017, the incidence rate in developed countries had gone down from the historic peak values while the incidence rate was still on the rise in developing counties. Given the aging trend in the globe, it is necessary to appeal to the public to decrease the exposure of kidney cancer-associated risk factors.

Comparison of the health risks associated with different exposure pathways of multiple volatile chlorinated hydrocarbons in contaminated drinking groundwater

A total of 152 groundwater samples were collected around a contaminated site to evaluate the carcinogenic and noncarcinogenic risks of exposure to twelve volatile chlorinated hydrocarbons (VCHs) by oral ingestion, dermal contact and inhalation absorption during showering. Although toxicity data of some VCHs are fragmentary, the results showed that the carcinogenic and noncarcinogenic risks of exposure to VCHs in contaminated drinking groundwater for local residents needs immediate attention. The main risk contributors for the carcinogenic and noncarcinogenic risks are carbon tetrachloride and 1,1,2-trichloroethane through inhalation exposure pathway, respectively. The health risk contribution rates associated with three exposure pathways for a specific VCH were intrinsic to the compound, and the dermal contact corresponded to a negligible contribution for almost every VCH species. Although most of the evaluated VCHs had a higher risk contribution by inhalation than by oral ingestion pathway, the integrated multi-VCH health risk contributions of the three exposure pathways were mainly dependent on the VCH compositions. Drinking boiled water not only decreased the exposure risk but also affected the risk contribution rates of three exposure pathways, which indicates that it is feasible to reduce the risk of VCH exposure during daily activities based on the risk contribution of the exposure pathways. In addition to the VCHs included in the drinking water standards, species such as 1,1,2,2-tetrachloroethane and hexachloroethane also showed a remarkable exposure health risk according to the standardized health risk calculation, which implied that improved drinking water standards are urgently required.

Prognostic biomarkers in renal cell carcinoma: is there a relationship with obesity?

Obesity is a recognized risk factor for renal cell carcinoma (RCC) the commonest form of kidney cancer. Both obesity and RCC are serious diseases with increasing incidence yearly. This review examined certain obesity associated measurements and adipokines as detection/prognostic indicators for RCC. The obesity related measurements such as body mass index (BMI), waist circumstance (WC), waist-hip ratio (WHR) in predicting RCC are valid when used in conjunction with other risk factors such as age and sex or with histological findings. The adipokine adiponectin holds promising outcomes as a predictive marker in assessing the risk of developing RCC. In addition, tissue leptin/leptin receptor may be a distinguishing marker for RCC subtypes. However, circulating leptin may not be a suitable detection or prognostic biomarker for RCC. The other less investigated adipokines; omentin, visfatin, apelin and resistin are also expressed in RCC but their prognostic capabilities are still inconclusive. BMI, WC and adipokines may be useful additions in a nomogram which includes TNM staging and pathological grading system to detect, confirm and follow-up RCC cases.

Incidence and mortality of kidney cancer: temporal patterns and global trends in 39 countries

We tested the hypotheses that kidney cancer incidence was increasing globally whilst its mortality was reducing; and its incidence was positively correlated with country-specific socioeconomic development. The incidence and mortality figures of each country were projected to 2030. Data on age-standardized incidence/mortality rates were retrieved from the GLOBOCAN in 2012. Temporal patterns were examined for 39 countries from the Cancer Incidence in Five Continents volumes I-X and other national registries. We evaluated the correlation between the incidence/mortality rates and Human Development Index (HDI)/Gross Domestic Product (GDP]). The average annual percent change of its incidence and mortality in the most recent 10 years was obtained from joinpoint regression. The highest incidence rates were observed in Eastern Europe and North America, while its mortality rates were the highest in European countries. Incidence was positively correlated with HDI and GDP per capita. Many countries experienced incidence rise over the most recent 10 years, and a substantial reduction in mortality rates was observed for a significant number of countries, yet increases in mortality rates were observed in Eastern Europe. By 2030, Brazil and Ecuador may have the greatest rise in incidence both in men and women, which requires urgent need for planning healthcare resources.

Imaging and Screening of Kidney Cancer

Renal cell carcinoma (RCC) exhibits a diverse and heterogeneous disease spectrum, but insight into its molecular biology has provided an improved understanding of potential risk factors, oncologic behavior, and imaging features. Computed tomography (CT) and MR imaging may allow the identification and preoperative subtyping of RCC and assessment of a response to various therapies. Active surveillance is a viable management option in some patients and has provided further insight into the natural history of RCC, including the favorable prognosis of cystic neoplasms. This article reviews CT and MR imaging in RCC and the role of screening in selected high-risk populations.

Occupational exposure to wood dust and risk of nasal and nasopharyngeal cancer: A case-control study among men in four nordic countries-With an emphasis on nasal adenocarcinoma

The current study aims to provide stronger evidence to aid in our understanding of the role of cumulative occupational exposure to (softwood-dominated) mixed wood dust in aetiology of nasal cancer. We included broad exposure occurred in a range of wood-processing occupation across varied industries in four Nordic countries. A population-based case-control study was conducted on all male cases with nasal adenocarcinoma (393 cases), other types of nasal cancer (2,446) and nasopharyngeal cancer (1,747) diagnosed in Finland, Sweden, Norway and Iceland between 1961 and 2005. For each case, five male controls, who were alive at the time of diagnosis of the case (index date), were randomly selected, matched by birth-year and country. Cumulative exposures (CE)s to wood dust and formaldehyde before the index date were quantified based on a job-exposure matrix linked to occupational titles derived from population censuses. Hazard ratios (HRs) for the CE of wood dust were estimated by conditional logistic regression, adjusted for CE to formaldehyde and 95% confidence intervals (CIs) were calculated. There was an increasing risk of nasal adenocarcinoma related to wood dust exposure. The HR in the highest CE category of wood dust (≥ 28.82 mg/m³ -years) was 16.5 (95% CI 5.05-54.1). Neither nonadenocarcinoma of the nose nor nasopharyngeal cancer could be linked to wood dust exposure. CE to softwood-dominated mixed wood dusts is strongly linked with elevated risk in nasal adenocarcinoma but not with other types of nasal or nasopharyngeal cancer.

Non‑infective occupational risk factors for hepatocellular carcinoma: A review (Review)

Liver cancer is the second leading worldwide cause of cancer‑associated mortalities. Hepatocellular carcinoma, which accounts for the majority of liver tumors, ranks fifth among types of human cancer. Well‑established risk factors for liver cancer include the hepatitis B and C viruses, aflatoxins, alcohol consumption, and oral contraceptives. Tobacco smoking, androgenic steroids, and diabetes mellitus are suspected risk factors. Current knowledge regarding non‑infective occupational risk factors for liver cancer is inconclusive. The relevance of liver disorders to occupational medicine lies in the fact that the majority of chemicals are metabolized in the liver, and toxic metabolites generated via metabolism are the predominant cause of liver damage. However, their non‑specific clinical manifestations that are similar in a number of liver diseases make diagnosis difficult. Furthermore, concomitant conditions, such as viral hepatitis and alcohol or drug abuse, may mask liver disorders that result from occupational hepatotoxic agents and block the demonstration of an occupational cause. The identification of environmental agents that result in human cancer is a long and often difficult process. The purpose of the present review is to summarize current knowledge regarding the association of non‑infective occupational risk exposure and HCC, to encourage further research and draw attention to this global occupational public health problem.

Comparison of hematological alterations and markers of B-cell activation in workers exposed to benzene, formaldehyde and trichloroethylene

Benzene, formaldehyde (FA) and trichloroethylene (TCE) are ubiquitous chemicals in workplaces and the general environment. Benzene is an established myeloid leukemogen and probable lymphomagen. FA is classified as a myeloid leukemogen but has not been associated with non-Hodgkin lymphoma (NHL), whereas TCE has been associated with NHL but not myeloid leukemia. Epidemiologic associations between FA and myeloid leukemia, and between benzene, TCE and NHL are, however, still debated. Previously, we showed that these chemicals are associated with hematotoxicity in cross-sectional studies of factory workers in China, which included extensive personal monitoring and biological sample collection. Here, we compare and contrast patterns of hematotoxicity, monosomy 7 in myeloid progenitor cells (MPCs), and B-cell activation biomarkers across these studies to further evaluate possible mechanisms of action and consistency of effects with observed hematologic cancer risks. Workers exposed to benzene or FA, but not TCE, showed declines in cell types derived from MPCs, including granulocytes and platelets. Alterations in lymphoid cell types, including B cells and CD4+ T cells, and B-cell activation markers were apparent in workers exposed to benzene or TCE. Given that alterations in myeloid and lymphoid cell types are associated with hematological malignancies, our data provide biologic insight into the epidemiological evidence linking benzene and FA exposure with myeloid leukemia risk, and TCE and benzene exposure with NHL risk.

Regional geographic variations in kidney cancer incidence rates in European countries

CONTEXT

Marked unexplained national variations in incidence rates of kidney cancer have been observed for decades in Europe.

OBJECTIVE

To investigate geographic variations at the regional level and identify European regions with high incidence rates of kidney cancer.

EVIDENCE ACQUISITION

Regional- and national-level incidence data were extracted from the Cancer Incidence in Five Continents databases, local cancer registry databases, and local published reports. World population age-standardised rates (ASRs) were calculated for the periods 2003-2007 and 1988-1992. Rates by period and sex were compared using map visualisation.

EVIDENCE SYNTHESIS

During 2003-2007, the highest ASR was found in the Plzen region, Czech Republic (31.4/100,000 person-years in men). Other regions of the Czech Republic had ASRs of 18.6-27.5/100,000 in men, with a tendency for higher rates in regions south of Prague. Surrounding regions, including eastern Germany and regions of Slovakia and Austria, had medium-to-high incidence rates (13.0-16.8/100,000 in men). Three other areas in Europe showed higher incidence rates in men compared with the rest of the continent: Lithuania, Estonia, Latvia, and Belarus (15.0-17.6/100,000); Iceland (13.5/100,000), and northern Italy (up to 16.0/100,000). Similar regional differences were observed among women, with rates approximately half of those observed in men in the same region. In general, these regional geographic variations remained stable over the periods 1988-1992 and 2003-2007, although higher incidence rates were detected in the Baltic countries in 2003-2007.

CONCLUSIONS

Several European regions show particularly high rates of kidney cancer incidence. Large variations were observed within countries covered by national health-care systems, implying that overdetection is not the major factor.

PATIENT SUMMARY

We present regional geographic variations in kidney cancer incidence rates in Europe. We highlight several regions with high incidence rates where further studies should be conducted for cancer control and prevention.

Occupational exposure to extremely low-frequency magnetic fields and electrical shocks and acute myeloid leukemia in four Nordic countries

OBJECTIVE

We studied the association between occupational exposure to extremely low-frequency magnetic fields (ELF-MF) and electrical shocks and acute myeloid leukemia (AML) in the Nordic Occupational Cancer cohort (NOCCA).

METHODS

We included 5,409 adult AML cases diagnosed between 1961 and 2005 in Finland, Iceland, Norway, and Sweden and 27,045 controls matched by age, sex, and country. Lifetime occupational ELF-MF exposure and risk of electrical shocks were assigned to jobs reported in the censuses using job-exposure matrices. We estimated hazard ratios (HRs) and 95 % confidence intervals (95 % CIs) using conditional logistic regression adjusted for concurrent occupational exposures relevant for AML risk (e.g., benzene, ionizing radiation). We conducted sensitivity analyses with different assumptions to assess the robustness of our results.

RESULTS

Approximately 40 % of the subjects were ever occupationally exposed to low levels and 7 % to high levels of ELF-MF, whereas 18 % were ever at low risk and 15 % at high risk of electrical shocks. We did not observe an association between occupational exposure to neither ELF-MF nor electrical shocks and AML. The HR was 0.88 (95 % CI 0.77-1.01) for subjects with high levels of ELF-MF exposure and 0.94 (95 % CI 0.85-1.05) for subjects with high risk of electrical shocks as compared to those with background-level exposure. Results remained materially unchanged in sensitivity analyses with different assumptions.

CONCLUSION

Our results do not support an association between occupational ELF-MF or electric shock exposure and AML.

Chlorinated volatile organic compounds (Cl-VOCs) in environment - sources, potential human health impacts, and current remediation technologies

Chlorinated volatile organic compounds (Cl-VOCs), including polychloromethanes, polychloroethanes and polychloroethylenes, are widely used as solvents, degreasing agents and a variety of commercial products. These compounds belong to a group of ubiquitous contaminants that can be found in contaminated soil, air and any kind of fluvial mediums such as groundwater, rivers and lakes. This review presents a summary of the research concerning the production levels and sources of Cl-VOCs, their potential impacts on human health as well as state-of-the-art remediation technologies. Important sources of Cl-VOCs principally include the emissions from industrial processes, the consumption of Cl-VOC-containing products, the disinfection process, as well as improper storage and disposal methods. Human exposure to Cl-VOCs can occur through different routes, including ingestion, inhalation and dermal contact. The toxicological impacts of these compounds have been carefully assessed, and the results demonstrate the potential associations of cancer incidence with exposure to Cl-VOCs. Most Cl-VOCs thus have been listed as priority pollutants by the Ministry of Environmental Protection (MEP) of China, Environmental Protection Agency of the U.S. (U.S. EPA) and European Commission (EC), and are under close monitor and strict control. Yet, more efforts will be put into the epidemiological studies for the risk of human exposure to Cl-VOCs and the exposure level measurements in contaminated sites in the future. State-of-the-art remediation technologies for Cl-VOCs employ non-destructive methods and destructive methods (e.g. thermal incineration, phytoremediation, biodegradation, advanced oxidation processes (AOPs) and reductive dechlorination), whose advantages, drawbacks and future developments are thoroughly discussed in the later sections.

Historical occupational trichloroethylene air concentrations based on inspection measurements from Shanghai, China

PURPOSE

Trichloroethylene (TCE) is a carcinogen that has been linked to kidney cancer and possibly other cancer sites including non-Hodgkin lymphoma. Its use in China has increased since the early 1990s with China's growing metal, electronic, and telecommunications industries. We examined historical occupational TCE air concentration patterns in a database of TCE inspection measurements collected in Shanghai, China to identify temporal trends and broad contrasts among occupations and industries.

METHODS

Using a database of 932 short-term, area TCE air inspection measurements collected in Shanghai worksites from 1968 through 2000 (median year 1986), we developed mixed-effects models to evaluate job-, industry-, and time-specific TCE air concentrations.

RESULTS

Models of TCE air concentrations from Shanghai work sites predicted that exposures decreased 5-10% per year between 1968 and 2000. Measurements collected near launderers and dry cleaners had the highest predicted geometric means (GM for 1986 = 150-190 mg m(-3)). The majority (53%) of the measurements were collected in metal treatment jobs. In a model restricted to measurements in metal treatment jobs, predicted GMs for 1986 varied 35-fold across industries, from 11 mg m(-3) in 'other metal products/repair' industries to 390 mg m(-3) in 'ships/aircrafts' industries.

CONCLUSIONS

TCE workplace air concentrations appeared to have dropped over time in Shanghai, China between 1968 and 2000. Understanding differences in TCE concentrations across time, occupations, and industries may assist future epidemiologic studies in China.

Occupational exposure to chlorinated and petroleum solvents and mycosis fungoides

OBJECTIVE

To evaluate the potential association between occupational exposure to chlorinated and petroleum solvents and mycosis fungoides (MF).

METHODS

A questionnaire on lifetime job history was administered to 100 patients diagnosed with MF and 2846 controls. Odds ratios (ORs) were calculated as the measure of the association between exposure to each specific solvent and MF.

RESULTS

In the total sample and in men, cases and controls did not differ in relation to exposure to any of the solvents studied. In women, an association with MF was seen for the highest level of estimated exposure to perchloroethylene (OR = 11.38; 95% confidence interval: 1.04 to 124.85) and for exposure less than the median to kerosene/fuel/gasoil (OR = 8.53; 95% confidence interval: 1.11 to 65.62).

CONCLUSIONS

These results do not provide conclusive evidence that exposure to solvents may increase risk of MF because they were not found in men.

Identification of serum biomarkers for occupational medicamentosa-like dermatitis induced by trichloroethylene using mass spectrometry

Occupational medicamentosa-like dermatitis induced by trichloroethylene (OMLDT) is an autoimmune disease and it has become a serious occupational health hazard. In the present study, we collected fasting blood samples from patients with OMLDT (n=18) and healthy volunteers (n=33) to explore serum peptidome patterns. Peptides in sera were purified using weak cation exchange magnetic beads (MB-WCX), and analyzed by matrix-assisted laser desorption ionization time-of-flight-mass spectrometry (MALDI-TOF-MS) and ClinProTools bioinformatics software. The intensities of thirty protein/peptide peaks were significantly different between the healthy control and OMLDT patients. A pattern of three peaks (m/z 2106.3, 2134.5, and 3263.67) was selected for supervised neural network (SNN) model building to separate the OMLDT patients from the healthy controls with a sensitivity of 95.5% and a specificity of 73.8%. Furthermore, two peptide peaks of m/z 4091.61 and 4281.69 were identified as fragments of ATP-binding cassette transporter family A member 12 (ABCA12), and cationic trypsinogen (PRRS1), respectively. Our findings not only show that specific proteomic fingerprints in the sera of OMLDT patients can be served as a differentiated tool of OMLDT patients with high sensitivity and high specificity, but also reveal the novel correlation between OMLDT with ABC transports and PRRS1, which will be of potential value for clinical and mechanistic studies of OMLDT.

The epidemiology of cancer among police officers

BACKGROUND

This review summarizes peer-reviewed studies examining cancer risks among police officers. It provides an overview of existing research limitations and uncertainties and the plausible etiologic risk factors associated with cancer in this understudied occupation.

METHODS

Previous cancer studies among police officers were obtained via a systematic review of the MEDLINE, CABDirect, and Web of Science bibliographic databases.

RESULTS

Quality observational studies of cancer among police officers are sparse and subject to limitations in exposure assessment and other methods. Results from three studies suggested possible increased mortality risks for all cancers, and cancers of the colon, kidney, digestive system, esophagus, male breast, and testis, as well as Hodgkin's disease. Few incidence studies have been performed, and results have been mixed, although some associations with police work have been observed for thyroid, skin, and male breast cancer.

CONCLUSIONS

Police are exposed to a mix of known or suspected agents or activities that increase cancer risk. Epidemiologic evidence to date is sparse and inconsistent. There is a critical need for more research to understand the biological and social processes underlying exposures and the suggested disproportionate risks and to identify effective prevention strategies.

Human health effects of trichloroethylene: key findings and scientific issues

BACKGROUND

In support of the Integrated Risk Information System (IRIS), the U.S. Environmental Protection Agency (EPA) completed a toxicological review of trichloroethylene (TCE) in September 2011, which was the result of an effort spanning > 20 years.

OBJECTIVES

We summarized the key findings and scientific issues regarding the human health effects of TCE in the U.S. EPA's toxicological review.

METHODS

In this assessment we synthesized and characterized thousands of epidemiologic, experimental animal, and mechanistic studies, and addressed several key scientific issues through modeling of TCE toxicokinetics, meta-analyses of epidemiologic studies, and analyses of mechanistic data.

DISCUSSION

Toxicokinetic modeling aided in characterizing the toxicological role of the complex metabolism and multiple metabolites of TCE. Meta-analyses of the epidemiologic data strongly supported the conclusions that TCE causes kidney cancer in humans and that TCE may also cause liver cancer and non-Hodgkin lymphoma. Mechanistic analyses support a key role for mutagenicity in TCE-induced kidney carcinogenicity. Recent evidence from studies in both humans and experimental animals point to the involvement of TCE exposure in autoimmune disease and hypersensitivity. Recent avian and in vitro mechanistic studies provided biological plausibility that TCE plays a role in developmental cardiac toxicity, the subject of substantial debate due to mixed results from epidemiologic and rodent studies.

CONCLUSIONS

TCE is carcinogenic to humans by all routes of exposure and poses a potential human health hazard for noncancer toxicity to the central nervous system, kidney, liver, immune system, male reproductive system, and the developing embryo/fetus.

The epidemiology and risk factors for renal cancer

BACKGROUND

Renal cancer is a frequently occurring malignancy with over 270,000 new cases diagnosed and it being responsible for 110,000 deaths annually on a global basis. Incidence rates have gradually increased whilst mortality rates are starting to plateau.

OBJECTIVE

To review epidemiology and risk factors for renal cancer.

METHODS

The current data is based on a thorough review of available original and review articles on epidemiology and risk factors for renal cancer with a systemic literature search utilising Medline.

RESULTS

The prevalence of associated risk factors such as genetic susceptibility, smoking, hypertension and obesity are changing and could account for the changes in incidence whilst the role of diet and occupational exposure to carcinogens requires further investigation.

CONCLUSION

Despite the evidence of various associated risk factors, further work is required from well designed studies to gain a greater understanding of the etiology of renal cancer.

Risk of hepatocellular carcinoma in workers exposed to chemicals

CONTEXT

Studies on experimental animals have shown liver is a common target of chemical carcinogens; this might suggest that occupational exposure to chemicals is another risk factor for HCC. However, the relationship between occupation and liver cancer has not been extensively studied, with the exception of the known association between vinyl chloride and angiosarcoma of the liver.

EVIDENCE ACQUISITION

A MEDLINE and conventional search of the past 50 years of the medical literature was performed to identify relevant articles on incidence and mechanisms of HCC due to occupational exposure to chemicals. Several important edited books and monographs were also identified and reviewed.

RESULTS

While laboratory data clearly indicate that the liver is an important target of chemical carcinogenesis, epidemiological studies provide very limited evidence on occupational risk factors for HCC. Nevertheless, we found some case reports and epidemiological data showing a moderately increased risk of HCC development in people exposed to vinyl chloride, organic solvents, pesticides, polychlorinated biphenyls, and arsenic.

CONCLUSIONS

Occupational exposure to chemicals may be another risk factor for HCC development, but the interpretation of currently available findings is limited by the small number of studies, questionable accuracy of the diagnosis of liver cancer, and potential confounding or modifying factors such as chronic hepatitis virus infection and alcohol consumption. Further relevant investigations are required for clarifying the actual contribution of occupational exposure to chemicals in HCC development.

Current understanding of lifestyle and environmental factors and risk of non-hodgkin lymphoma: an epidemiological update

The incidence rates of non-Hodgkin lymphoma (NHL) have steadily increased over the last several decades in the United States, and the temporal trends in incidence can only be partially explained by the HIV epidemic. In 1992, an international workshop sponsored by the United States National Cancer Institute concluded that there was an “emerging epidemic” of NHL and emphasized the need to investigate the factors responsible for the increasing incidence of this disease. Over the past two decades, numerous epidemiological studies have examined the risk factors for NHL, particularly for putative environmental and lifestyle risk factors, and international consortia have been established in order to investigate rare exposures and NHL subtype-specific associations. While few consistent risk factors for NHL aside from immunosuppression and certain infectious agents have emerged, suggestive associations with several lifestyle and environmental factors have been reported in epidemiologic studies. Further, increasing evidence has suggested that the effects of these and other exposures may be limited to or stronger for particular NHL subtypes. This paper examines the progress that has been made over the last twenty years in elucidating the etiology of NHL, with a primary emphasis on lifestyle factors and environmental exposures.

Concentration of trichloroethylene in breast milk and household water from Nogales, Arizona

The United States Environmental Protection Agency has identified quantification of trichloroethylene (TCE), an industrial solvent, in breast milk as a high priority need for risk assessment. Water and milk samples were collected from 20 households by a lactation consultant in Nogales, Arizona. Separate water samples (including tap, bottled, and vending machine) were collected for all household uses: drinking, bathing, cooking, and laundry. A risk factor questionnaire was administered. Liquid-liquid extraction with diethyl ether was followed by GC-MS for TCE quantification in water. Breast milk underwent homogenization, lipid hydrolysis, and centrifugation prior to extraction. The limit of detection was 1.5 ng/mL. TCE was detected in 7 of 20 mothers' breast milk samples. The maximum concentration was 6 ng/mL. TCE concentration in breast milk was significantly correlated with the concentration in water used for bathing (ρ = 0.59, p = 0.008). Detection of TCE in breast milk was more likely if the infant had a body mass index <14 (RR = 5.2, p = 0.02). Based on average breast milk consumption, TCE intake for 5% of the infants may exceed the proposed U.S. EPA Reference Dose. Results of this exploratory study warrant more in depth studies to understand risk of TCE exposures from breast milk intake.

Using bioinformatic approaches to identify pathways targeted by human leukemogens

We have applied bioinformatic approaches to identify pathways common to chemical leukemogens and to determine whether leukemogens could be distinguished from non-leukemogenic carcinogens. From all known and probable carcinogens classified by IARC and NTP, we identified 35 carcinogens that were associated with leukemia risk in human studies and 16 non-leukemogenic carcinogens. Using data on gene/protein targets available in the Comparative Toxicogenomics Database (CTD) for 29 of the leukemogens and 11 of the non-leukemogenic carcinogens, we analyzed for enrichment of all 250 human biochemical pathways in the Kyoto Encyclopedia of Genes and Genomes (KEGG) database. The top pathways targeted by the leukemogens included metabolism of xenobiotics by cytochrome P450, glutathione metabolism, neurotrophin signaling pathway, apoptosis, MAPK signaling, Toll-like receptor signaling and various cancer pathways. The 29 leukemogens formed 18 distinct clusters comprising 1 to 3 chemicals that did not correlate with known mechanism of action or with structural similarity as determined by 2D Tanimoto coefficients in the PubChem database. Unsupervised clustering and one-class support vector machines, based on the pathway data, were unable to distinguish the 29 leukemogens from 11 non-leukemogenic known and probable IARC carcinogens. However, using two-class random forests to estimate leukemogen and non-leukemogen patterns, we estimated a 76% chance of distinguishing a random leukemogen/non-leukemogen pair from each other.

Decreased Numbers of CD4(+) Naive and Effector Memory T Cells, and CD8(+) Naïve T Cells, are Associated with Trichloroethylene Exposure

Trichloroethylene (TCE) is a volatile chlorinated organic compound that is commonly used as a solvent for lipophilic compounds. Although recognized as an animal carcinogen, TCE's carcinogenic potential in humans is still uncertain. We have carried out a cross-sectional study of 80 workers exposed to TCE and 96 unexposed controls matched on age and sex in Guangdong, China to study TCE's early biologic effects. We previously reported that the total lymphocyte count and each of the major lymphocyte subsets (i.e., CD4(+) T cells, CD8(+) T cells, natural killer cells, and B cells) were decreased in TCE-exposed workers compared to controls, suggesting a selective effect on lymphoid progenitors, and/or lymphocyte survival. To explore which T lymphocyte subsets are affected in the same study population, we investigated the effect of TCE exposure on the numbers of CD4(+) naïve and memory T cells, CD8(+) naïve and memory T cells, and regulatory T cells by FACS analysis. Linear regression of each subset was used to test for differences between exposed workers and controls adjusting for potential confounders. We observed that CD4(+) and CD8(+) naïve T cell counts were about 8% (p = 0.056) and 17% (p = 0.0002) lower, respectively, among exposed workers. CD4(+) effector memory T cell counts were decreased by about 20% among TCE-exposed workers compared to controls (p = 0.001). The selective targeting of TCE on CD8(+) naive and possibly CD4(+) naive T cells, and CD4(+) effector memory T cells, provide further insights into the immunosuppression-related response of human immune cells upon TCE exposure.

Epidemiology of renal cell cancer

Renal cell cancer (RCC) is increasingly diagnosed at an early stage in many countries, which likely contributes to the recent leveling of RCC mortality in the United States and many European countries. However, over all stages nearly 50% of the patients die within 5 years after diagnosis. Smoking and obesity may account for approximately 40% of all incidental cases in high-risk countries. Besides obesity, rising prevalence of hypertension may play a growing role. Several other occupational and lifestyle factors may also affect the risk of RCC. Genetic variations may be an important factor in the differing incidence among populations.

Trichloroethylene and cancer: systematic and quantitative review of epidemiologic evidence for identifying hazards

We conducted a meta-analysis focusing on studies with high potential for trichloroethylene (TCE) exposure to provide quantitative evaluations of the evidence for associations between TCE exposure and kidney, liver, and non-Hodgkin lymphoma (NHL) cancers. A systematic review documenting essential design features, exposure assessment approaches, statistical analyses, and potential sources of confounding and bias identified twenty-four cohort and case-control studies on TCE and the three cancers of interest with high potential for exposure, including five recently published case-control studies of kidney cancer or NHL. Fixed- and random-effects models were fitted to the data on overall exposure and on the highest exposure group. Sensitivity analyses examined the influence of individual studies and of alternative risk estimate selections. For overall TCE exposure and kidney cancer, the summary relative risk (RRm) estimate from the random effects model was 1.27 (95% CI: 1.13, 1.43), with a higher RRm for the highest exposure groups (1.58, 95% CI: 1.28, 1.96). The RRm estimates were not overly sensitive to alternative risk estimate selections or to removal of an individual study. There was no apparent heterogeneity or publication bias. For NHL, RRm estimates for overall exposure and for the highest exposure group, respectively, were 1.23 (95% CI: 1.07, 1.42) and 1.43 (95% CI: 1.13, 1.82) and, for liver cancer, 1.29 (95% CI: 1.07, 1.56) and 1.28 (95% CI: 0.93, 1.77). Our findings provide strong support for a causal association between TCE exposure and kidney cancer. The support is strong but less robust for NHL, where issues of study heterogeneity, potential publication bias, and weaker exposure-response results contribute uncertainty, and more limited for liver cancer, where only cohort studies with small numbers of cases were available.

Insights from epidemiology into dichloromethane and cancer risk

Dichloromethane (methylene chloride) is a widely used chlorinated solvent. We review the available epidemiology studies (five cohort studies, 13 case-control studies, including seven of hematopoietic cancers), focusing on specific cancer sites. There was little indication of an increased risk of lung cancer in the cohort studies (standardized mortality ratios ranging from 0.46 to 1.21). These cohorts are relatively small, and variable effects (e.g., point estimates ranging from 0.5 to 2.0) were seen for the rarer forms of cancers such as brain cancer and specific hematopoietic cancers. Three large population-based case-control studies of incident non-Hodgkin lymphoma in Europe and the United States observed odds ratios between 1.5 and 2.2 with dichloromethane exposure (ever exposed or highest category of exposure), with higher risk seen in specific subsets of disease. More limited indications of associations with brain cancer, breast cancer, and liver and biliary cancer were also seen in this collection of studies. Existing cohort studies, given their size and uneven exposure information, are unlikely to resolve questions of cancer risks and dichloromethane exposure. More promising approaches are population-based case-control studies of incident disease, and the combination of data from such studies, with robust exposure assessments that include detailed occupational information and exposure assignment based on industry-wide surveys or direct exposure measurements.

Is exposure to formaldehyde in air causally associated with leukemia?--A hypothesis-based weight-of-evidence analysis

Recent scientific debate has focused on the potential for inhaled formaldehyde to cause lymphohematopoietic cancers, particularly leukemias, in humans. The concern stems from certain epidemiology studies reporting an association, although particulars of endpoints and dosimetry are inconsistent across studies and several other studies show no such effects. Animal studies generally report neither hematotoxicity nor leukemia associated with formaldehyde inhalation, and hematotoxicity studies in humans are inconsistent. Formaldehyde's reactivity has been thought to preclude systemic exposure following inhalation, and its apparent inability to reach and affect the target tissues attacked by known leukemogens has, heretofore, led to skepticism regarding its potential to cause human lymphohematopoietic cancers. Recently, however, potential modes of action for formaldehyde leukemogenesis have been hypothesized, and it has been suggested that formaldehyde be identified as a known human leukemogen. In this article, we apply our hypothesis-based weight-of-evidence (HBWoE) approach to evaluate the large body of evidence regarding formaldehyde and leukemogenesis, attending to how human, animal, and mode-of-action results inform one another. We trace the logic of inference within and across all studies, and articulate how one could account for the suite of available observations under the various proposed hypotheses. Upon comparison of alternative proposals regarding what causal processes may have led to the array of observations as we see them, we conclude that the case for a causal association is weak and strains biological plausibility. Instead, apparent association between formaldehyde inhalation and leukemia in some human studies is better interpreted as due to chance or confounding.

Occupational exposure to trichloroethylene and cancer risk for workers at the Paducah Gaseous Diffusion Plant

OBJECTIVE

The Paducah Gaseous Diffusion Plant (PGDP) became operational in 1952; it is located in the western part of Kentucky. We conducted a mortality study for adverse health effects that workers may have suffered while working at the plant, including exposures to chemicals.

MATERIALS AND METHODS

We studied a cohort of 6820 workers at the PGDP for the period 1953 to 2003; there were a total of 1672 deaths to cohort members. Trichloroethylene (TCE) is a specific concern for this workforce; exposure to TCE occurred primarily in departments that clean the process equipment. The Life Table Analysis System (LTAS) program developed by NIOSH was used to calculate the standardized mortality ratios for the worker cohort and standardized rate ratio relative to exposure to TCE (the U.S. population is the referent for ageadjustment). LTAS calculated a significantly low overall SMR for these workers of 0.76 (95% CI: 0.72-0.79). A further review of three major cancers of interest to Kentucky produced significantly low SMR for trachea, bronchus, lung cancer (0.75, 95% CI: 0.72-0.79) and high SMR for Non-Hodgkin's lymphoma (NHL) (1.49, 95% CI: 1.02-2.10).

RESULTS

No significant SMR was observed for leukemia and no significant SRRs were observed for any disease. Both the leukemia and lung cancer results were examined and determined to reflect regional mortality patterns. However, the Non-Hodgkin's Lymphoma finding suggests a curious amplification when living cases are included with the mortality experience.

CONCLUSIONS

Further examination is recommended of this recurrent finding from all three U.S. Gaseous Diffusion plants.

Enhancement of immediate allergic reactions by trichloroethylene ingestion via drinking water in mice

The prevalence of allergic disorders is increasing in industrial areas and countries. Recent reports suggest that some environmental pollutants are related to the increase in allergic diseases, and we reported that trichloroethylene (TCE) is a candidate chemical for causing the increase of allergic diseases, as TCE ingestion is associated with allergic reaction enhancement. TCE is widely used in many industries, and it is commonly detected as an environmental contaminant. This study aimed to clarify the immunotoxicity of TCE in detail. BALB/c mice were treated with TCE dissolved in drinking water for 2 and 4 weeks, and the mice were immunized with ovalbumin (OVA)/aluminum hydroxide (alum) twice. On the final day of the TCE exposure period, we measured the active cutaneous anaphylaxis (ACA) reaction and the antigen- specific IgE level in serum as well as the histamine level at the allergic reaction site and assayed the proliferation rates of splenocytes collected from the animals. The ACA reaction was enhanced by TCE ingestion. The OVA specific IgE level in mice was enhanced by TCE exposure for 4 weeks. The proliferation rate of the splenocytes was enhanced by TCE ingestion for 2 and 4 weeks. The enhancement of the ACA reaction by TCE ingestion via drinking water may be related to the increase in splenocyte proliferation. On the other hand, it may be weakly related to antigen-specific IgE production.

A case-control study of occupational exposure to trichloroethylene and non-Hodgkin lymphoma

BACKGROUND

Previous epidemiologic findings suggest an association between exposure to trichloroethylene (TCE), a chlorinated solvent primarily used for vapor degreasing of metal parts, and non-Hodgkin lymphoma (NHL).

OBJECTIVES

We investigated the association between occupational TCE exposure and NHL within a population-based case-control study using detailed exposure assessment methods.

METHODS

Cases (n = 1,189; 76% participation rate) and controls (n = 982; 52% participation rate) provided information on their occupational histories and, for selected occupations, on possible workplace exposure to TCE using job-specific interview modules. An industrial hygienist assessed potential TCE exposure based on this information and a review of the TCE industrial hygiene literature. We computed odds ratios (ORs) and 95% confidence intervals (CIs) relating NHL and different metrics of estimated TCE exposure, categorized using tertiles among exposed controls, with unexposed subjects as the reference group.

RESULTS

We observed associations with NHL for the highest tertiles of estimated average weekly exposure (23 exposed cases; OR = 2.5; 95% CI, 1.1–6.1) and cumulative exposure (24 exposed cases; OR = 2.3; 95% CI, 1.0-5.0) to TCE. Tests for trend with these metrics surpassed or approached statistical significance (p-value for trend = 0.02 and 0.08, respectively); however, we did not observe dose–response relationships across the exposure levels. Overall, neither duration nor intensity of exposure was associated with NHL, although we observed an association with the lowest tertile of exposure duration (OR = 2.1; 95% CI, 1.0-4.7).

CONCLUSIONS

Our findings offer additional support for an association between high levels of exposure to TCE and increased risk of NHL. However, we cannot rule out the possibility of confounding from other chlorinated solvents used for vapor degreasing and note that our exposure assessment methods have not been validated.

Occupational exposure to trichloroethylene is associated with a decline in lymphocyte subsets and soluble CD27 and CD30 markers

Occupational cohort and case-control studies suggest that trichloroethylene (TCE) exposure may be associated with non-Hodgkin lymphoma (NHL) but findings are not consistent. There is a need for mechanistic studies to evaluate the biologic plausibility of this association. We carried out a cross-sectional molecular epidemiology study of 80 healthy workers that used TCE and 96 comparable unexposed controls in Guangdong, China. Personal exposure measurements were taken over a three-week period before blood collection. Ninety-six percent of workers were exposed to TCE below the current US Occupational Safety and Health Administration Permissible Exposure Limit (100 p.p.m. 8 h time-weighted average), with a mean (SD) of 22.2 (36.0) p.p.m. The total lymphocyte count and each of the major lymphocyte subsets including CD4+ T cells, CD8+ T cells, natural killer (NK) cells and B cells were significantly decreased among the TCE-exposed workers compared with controls (P < 0.05), with evidence of a dose-dependent decline. Further, there was a striking 61% decline in sCD27 plasma level and a 34% decline in sCD30 plasma level among TCE-exposed workers compared with controls. This is the first report that TCE exposure under the current Occupational Safety and Health Administration workplace standard is associated with a decline in all major lymphocyte subsets and sCD27 and sCD30, which play an important role in regulating cellular activity in subsets of T, B and NK cells and are associated with lymphocyte activation. Given that altered immunity is an established risk factor for NHL, these results add to the biologic plausibility that TCE is a possible lymphomagen.

Epidemiology and risk factors for kidney cancer

After more than two decades of rising rates, in recent years the total kidney cancer incidence worldwide has shown signs of stabilizing, or even decreasing. In adults, kidney cancer consists of renal cell carcinoma (RCC), the predominant form, and renal transitional cell carcinoma (RTCC); these types primarily arise in the renal parenchyma and renal pelvis, respectively. Although temporal trends by kidney cancer type are not well established worldwide, incidence of RCC in the US has continued to rise, mainly for early-stage tumors, while that of RTCC has declined, and total kidney cancer mortality rates have leveled. Stabilization of kidney cancer mortality rates has also been reported in Europe. These trends are consistent with reports of increasing incidental diagnoses and a downward shift in tumor stage and size in clinical series. The changing prevalence of known risk factors for RCC, including cigarette smoking, obesity, and hypertension, is also likely to affect incidence trends, although their relative impact may differ between populations. Accumulating evidence suggests an etiologic role in RCC for physical activity, alcohol consumption, occupational exposure to trichloroethylene, and high parity among women, but further research is needed into the potential causal effects of these factors. Genetic factors and their interaction with environmental exposures are believed to influence risk of developing RCC, but a limited number of studies using candidate-gene approaches have not produced conclusive results. Large consortium efforts employing genome-wide scanning technology are underway, which hold promise for novel discoveries in renal carcinogenesis.

Cysteine S-conjugate β-lyases: important roles in the metabolism of naturally occurring sulfur and selenium-containing compounds, xenobiotics and anticancer agents

Cysteine S-conjugate β-lyases are pyridoxal 5'-phosphate-containing enzymes that catalyze β-elimination reactions with cysteine S-conjugates that possess a good leaving group in the β-position. The end products are aminoacrylate and a sulfur-containing fragment. The aminoacrylate tautomerizes and hydrolyzes to pyruvate and ammonia. The mammalian cysteine S-conjugate β-lyases thus far identified are enzymes involved in amino acid metabolism that catalyze β-lyase reactions as non-physiological side reactions. Most are aminotransferases. In some cases the lyase is inactivated by reaction products. The cysteine S-conjugate β-lyases are of much interest to toxicologists because they play an important key role in the bioactivation (toxication) of halogenated alkenes, some of which are produced on an industrial scale and are environmental contaminants. The cysteine S-conjugate β-lyases have been reviewed in this journal previously (Cooper and Pinto in Amino Acids 30:1-15, 2006). Here, we focus on more recent findings regarding: (1) the identification of enzymes associated with high-M(r) cysteine S-conjugate β-lyases in the cytosolic and mitochondrial fractions of rat liver and kidney; (2) the mechanism of syncatalytic inactivation of rat liver mitochondrial aspartate aminotransferase by the nephrotoxic β-lyase substrate S-(1,1,2,2-tetrafluoroethyl)-L-cysteine (the cysteine S-conjugate of tetrafluoroethylene); (3) toxicant channeling of reactive fragments from the active site of mitochondrial aspartate aminotransferase to susceptible proteins in the mitochondria; (4) the involvement of cysteine S-conjugate β-lyases in the metabolism/bioactivation of drugs and natural products; and (5) the role of cysteine S-conjugate β-lyases in the metabolism of selenocysteine Se-conjugates. This review emphasizes the fact that the cysteine S-conjugate β-lyases are biologically more important than hitherto appreciated.

Trichloroethylene risk assessment: a review and commentary

Trichloroethylene (TCE) is a widespread environmental contaminant that is carcinogenic when given in high, chronic doses to certain strains of mice and rats. The capacity of TCE to cause cancer in humans is less clear. The current maximum contaminant level (MCL) of 5 ppb (microg/L) is based on an US Environment Protection Agency (USEPA) policy decision rather than the underlying science. In view of major advances in understanding the etiology and mechanisms of chemically induced cancer, USEPA began in the late 1990s to revise its guidelines for cancer risk assessment. TCE was chosen as the pilot chemical. The USEPA (2005) final guidelines emphasized a "weight-of-evidence" approach with consideration of dose-response relationships, modes of action, and metabolic/toxicokinetic processes. Where adequate data are available to support reversible binding of the carcinogenic moiety to biological receptors as the initiating event (i.e., a threshold exists), a nonlinear approach is to be used. Otherwise, the default assumption of a linear (i.e., nonthreshold) dose-response is utilized. When validated physiologically based pharmacokinetic (PBPK) models are available, they are to be used to predict internal dosimetry as the basis for species and dose extrapolations. The present article reviews pertinent literature and discusses areas where research may resolve some outstanding issues and facilitate the reassessment process. Key research needs are proposed, including role of dichloroacetic acid (DCA) in TCE-induced liver tumorigenesis in humans; extension of current PBPK models to predict target organ deposition of trichloroacetic acid (TCA) and DCA in humans ingesting TCE in drinking water; use of human hepatocytes to ascertain metabolic rate constants for use in PBPK models that incorporate variability in metabolism of TCE by potentially sensitive subpopulations; measurement of the efficiency of first-pass elimination of trace levels of TCE in drinking water; and assessment of exogenous factors' (e.g., alcohol, drugs) ability to alter metabolic activation and risks at such low-level exposure.

Environmental factors in cancer: trichloroethylene and related solvents: science, regulation, and cancer prevention

In summary, I have used the case of TCE exposure as an example of: (1) The importance of population-based research to identify and characterize possible environmental risk factors for cancer, and the need for a greater emphasis and proportional increase in public funding of research on prevention as compared to treatment. We need to understand these risks better, and use this information to drive effective public health prevention actions. (2) The imposition of strong restrictions on requests by bona fide researchers for access to data as a barrier to research that could be used to help resolve some of the most controversial issues in TCE epidemiology, in particular, and environmental risks in general, especially access to individual level data including data of event and location of residence. Researchers need ready access these data to more accurately characterize environmental exposures, diseases and their possible associations, and to help develop more effective public health preventive actions, although they should also protect confidentiality. (3) The need for more accurate and comprehensive biomarkers of exposure and disease to better assess possible associations between environmental and occupational exposures and disease; (4) The role of non-scientific concerns in limiting regulatory and advisory agencies in the reevaluation of their positions relative to preventing or lowering allowable exposures to TCE, in light of the growing body of evidence on the possible carcinogenicity of a compound still widely in use, to which many workers, and substantial segments of the general public, are exposed.

Toxicity, biomarkers, genotoxicity, and carcinogenicity of trichloroethylene and its metabolites: a review

Trichloroethylene (TCE) is a prevalent occupational and environmental contaminant that has been reported to cause a variety of toxic effects. This article reviews toxicity, mutagenicity, and carcinogenicity caused by the exposure of TCE and its metabolites in the living system as well as on their (TCE and its metabolites) toxicity biomarkers.

Risk of liver cancer and exposure to organic solvents and gasoline vapors among Finnish workers

We investigated the association between exposure to various groups of solvents and gasoline vapors and liver cancer. A cohort of economically active Finns born between 1906 and 1945 was followed up during the period 1971-1995. The incident cases of primary liver cancer (n = 2474) were identified in a record linkage with the Finnish Cancer Registry. Occupations from the 1970 census were converted to exposures using a job-exposure matrix. Cumulative exposure was calculated as the product of estimated prevalence, level and duration of exposure, and we used Poisson regression to calculate the relative risks (RR). Among the occupations entailing exposure to organic solvents, an elevated liver cancer incidence was observed in male printers, and varnishers and lacquerers. Among men, the risk was increased in the highest exposure category of aromatic hydrocarbons [RR 1.77, 95% confidence interval (CI) 1.30-2.40], aliphatic/alicyclic hydrocarbons (RR 1.47, 95% CI 0.99-2.18), chlorinated hydrocarbons (RR 2.65, 95% CI 1.38-5.11) and "other solvents" (RR 2.14, 95% CI 1.23-3.71). Among women, the risk was increased for the group "other solvents" that includes mainly alcohols, ketones, esters and glycol ethers (RR 2.73, 95% CI 1.21-6.16). Our finding of an increased risk among workers exposed to chlorinated hydrocarbons is in line with several earlier studies on trichloroethylene. The results also suggest a link between exposure to other types of solvents and the risk of liver cancer. The possibility that alcohol consumption contributes to the observed risks cannot be totally excluded.

Trichloroethylene liver toxicity in mouse and rat: microarray analysis reveals species differences in gene expression

Trichloroethylene (TCE), an industrial organic solvent found in the environment, is a known carcinogen in laboratory animals and is believed to be carcinogenic in humans. Its carcinogenicity is subject to species-specific differences in biological activity, causing hepatocellular carcinoma in mouse and renal-cell carcinoma in rat. We have sought to better understand TCE's mode of action (MOA) by studying the alterations in gene expression profiles of liver in mice and rats that were administrated TCE by oral gavage either once or daily for 14 days. Microarray analysis revealed distinct transcriptional profiles and differences in biological pathways not only species-specific, but also pulse-dose effects within each species. For example, inhibition of the TGF-beta pathway and activation of MAPK signaling were specific to mice repeatedly exposed to TCE. A better understanding of the MOA in mice and rats will lead to better hypotheses of TCE's affect on humans.