Assessment of the developmental risks resulting from occupational exposure to select glycol ethers within the semiconductor industry

Assessment of Occupational Health Risks for Maintenance Work in Fabrication Facilities: Brief Review and Recommendations

Background

This study focuses on assessing occupational risk for the health hazards encountered during maintenance works (MW) in semiconductor fabrication (FAB) facilities.

Objectives

The objectives of this study include: 1) identifying the primary health hazards during MW in semiconductor FAB facilities; 2) reviewing the methods used in evaluating the likelihood and severity of health hazards through occupational health risk assessment (OHRA); and 3) suggesting variables for the categorization of likelihood of exposures to health hazards and the severity of health effects associated with MW in FAB facilities.

Methods

A literature review was undertaken on OHRA methodology and health hazards resulting from MW in FAB facilities. Based on this review, approaches for categorizing the exposure to health hazards and the severity of health effects related to MW were recommended.

Results

Maintenance workers in FAB facilities face exposure to hazards such as debris, machinery entanglement, and airborne particles laden with various chemical components. The level of engineering and administrative control measures is suggested to assess the likelihood of simultaneous chemical and dust exposure. Qualitative key factors for mixed exposure estimation during MW include the presence of safe operational protocols, the use of air-jet machines, the presence and effectiveness of local exhaust ventilation system, chamber post-purge and cooling, and proper respirator use. Using the risk (R) and hazard (H) codes of the Globally Harmonized System alongside carcinogenic, mutagenic, or reprotoxic classifications aid in categorizing health effect severity for OHRA.

Conclusion

Further research is needed to apply our proposed variables in OHRA for MW in FAB facilities and subsequently validate the findings.

Biomonitoring of Exposures to Solvents and Metals in Electronics Manufacturing Facilities in Batam, Indonesia

Concerns about chemical exposure in the electronics manufacturing industry have long been recognized, but data are lacking in Southeast Asia. We conducted a study in Batam, Indonesia, to evaluate chemical exposures in electronics facilities, using participatory research and biological monitoring approaches. A convenience sample of 36 workers (28 exposed, 8 controls) was recruited, and urine samples were collected before and after shifts. Five solvents (acetone, methyl ethyl ketone, toluene, benzene, and xylenes) were found in 46%-97% of samples, and seven metals (arsenic, cadmium, cobalt, tin, antimony, lead, and vanadium) were detected in 60%-100% of samples. Biological monitoring and participatory research appeared to be useful in assessing workers' exposure when workplace air monitoring is not feasible due to a lack of cooperation from the employer. Several logistical challenges need to be addressed in future biomonitoring studies of electronics workers in Asia in factories where employers are reluctant to track workers' exposure and health.

Ethylene oxide derived glycol ethers: A review of the alkyl glycol ethers potential to cause endocrine disruption

The 'ethylene glycol ethers' (EGE) are a broad family of solvents and hydraulic fluids produced through the reaction of ethylene oxide and a monoalcohol. Certain EGE derived from methanol and ethanol are well known to cause toxicity to the testes and fetotoxicity and that this is caused by the common metabolites methoxy and ethoxyacetic acid, respectively. There have been numerous published claims that EGE fall into the category of 'endocrine disruptors' often without substantiated evidence. This review systematically evaluates all of the available and relevant in vitro and in vivo data across this family of substances using an approach based around the EFSA/ECHA 2018 guidance for the identification of endocrine disruptors. The conclusion reached is that there is no significant evidence to show that EGE target any endocrine organs or perturb endocrine pathways and that any toxicity that is seen occurs by non-endocrine modes of action.

The urinary metabolic profile of diethylene glycol methyl ether and triethylene glycol methyl ether in Sprague-Dawley rats and the role of the metabolite methoxyacetic acid in their toxicity

Ethylene glycol ethers are a well-known series of solvents and hydraulic fluids derived from the reaction of ethylene oxide and monoalcohols. Use of methanol as the alcohol results in a series of mono, di and triethylene glycol methyl ethers. The first in the series, monoethylene glycol methyl ether (EGME or 2-methoxyethanol) is well characterised and metabolises in vivo to methoxyacetic acid (MAA), a known reproductive toxicant. Metabolism data is not available for the di and triethylene glycol ethers (DEGME and TEGME respectively). This study evaluated the metabolism of these two substances in male rats following single oral gavage doses of 500, 1000 and 2000 mg/kg for DEGME and 1000 mg/kg for TEGME. As for EGME, the dominant metabolite of each was the acid metabolite derived by oxidation of the terminal hydroxyl group. Elimination of these metabolites was rapid, with half-lives <4 h for each one. Both substances were also found to produce small amounts of MAA (~0.5% for TEGME and ~1.1% for DEGME at doses of 1000 mg/kg) through cleavage of the ether groups in the molecules. These small amounts of MAA produced can explain the effects seen at high doses in reproductive studies using DEGME and TEGME.

The toxicity of crude 4-methylcyclohexanemethanol (MCHM): review of experimental data and results of predictive models for its constituents and a putative metabolite

Crude 4-methylcyclohexanemethanol (MCHM) is an industrial solvent used to clean coal. Approximately 10 000 gallons of a liquid mixture containing crude MCHM were accidently released into the Elk River in West Virginia in January 2014. Because of the proximity to a water treatment facility, the contaminated water was distributed to approximately 300 000 residents. In this review, experimental data and computational predictions for the toxicity for crude MCHM, distilled MCHM, its other components and its putative metabolites are presented. Crude MCHM, its other constituents and its metabolites have low to moderate acute and subchronic oral toxicity. Crude MCHM has been shown not to be a skin sensitizer below certain doses, indicating that at plausible human exposures it does not cause an allergic response. Crude MCHM and its constituents cause slight to moderate skin and eye irritation in rodents at high concentrations. These chemicals are not mutagenic and are not predicted to be carcinogenic. Several of the constituents were predicted through modeling to be possible developmental toxicants; however, 1,4-cyclohexanedimethanol, 1,4-cyclohexanedicarboxylic acid and dimethyl 1,4-cyclohexanedicarboxylate did not demonstrate developmental toxicity in rat studies. Following the spill, the Centers for Disease Control and Prevention recommended a short-term health advisory level of 1 ppm for drinking water that it determined was unlikely to be associated with adverse health effects. Crude MCHM has an odor threshold lower than 10 ppb, indicating that it could be detected at concentrations at least 100-fold less than this risk criterion. Collectively, the findings and predictions indicate that crude MCHM poses no apparent toxicological risk to humans at 1 ppm in household water.

The health impacts of semiconductor production: an epidemiologic review

BACKGROUND

Despite concerns over the harmful health effects of semiconductor production, epidemiological studies have shown mixed results.

OBJECTIVES

We aim to critically appraise epidemiologic studies to date, and to suggest future research and actions to protect workers in semiconductor industry.

METHODS

Epidemiologic studies were identified through electronic database searches, review of reference lists of relevant published works, and expert consultations, and were narratively reviewed.

RESULTS

Most evidence suggests reproductive risks from fabrication jobs, including spontaneous abortion (SAB), congenital malformation, and reduced fertility. Although chemicals have been suspected as causal agents, knowledge of the likely contribution(s) from specific exposures is still limited. Evidence of cancer risk seems to be equivocal. However, the available studies had serious limitations including healthy worker effects (HWEs), information bias, and insufficient power, all of which are associated with underestimation. Nevertheless, excess risks for non-Hodgkin's lymphoma (NHL), leukemia, brain tumor, and breast cancer were observed.

CONCLUSIONS

Monitoring and innovative research based on international collaboration with a focus on sentinel events are required.

Worker exposure to methanol vapors during cleaning of semiconductor wafers in a manufacturing setting

An exposure simulation was conducted to characterize methanol exposure of workers who cleaned wafers in quality control departments within the semiconductor industry. Short-term (15 min) and long-term (2-4 hr) personal and area samples (at distances of 1 m and 3-6 m from the source) were collected during the 2-day simulation. On the first day, 45 mL of methanol were used per hour by a single worker washing wafers in a 102 m(3) room with a ventilation rate of about 10 air changes per hour (ACH). Virtually all methanol volatilized. To assess exposures under conditions associated with higher productivity, on the second day, two workers cleaned wafers simultaneously, together using methanol at over twice the rate of the first day (95 mL/hr). On this day, the ventilation rate was halved (5 ACH). Personal concentrations on the first day averaged 60 ppm (SD = 46 ppm) and ranged from 10-140 ppm. On the second day, personal concentrations for both workers averaged 118 ppm (SD = 50 ppm; range: 64-270 ppm). Area concentrations measured on the first day at 1 m from the source and throughout the balance of the room averaged 29 ppm (SD = 19 ppm; range: 4-83 ppm) and 18 ppm (SD = 12 ppm; range: 3-42 ppm), respectively. As expected, area concentrations measured on the second day were higher than the first and averaged 73 ppm (SD = 25 ppm; range: 27-140 ppm) at 1 meter and 48 ppm (SD = 13 ppm; range: 21-67 ppm) throughout the balance of the room. The results of this simulation suggest that the use of methanol to clean semiconductor wafers without the use of local exhaust ventilation and with relatively low room ventilation rates is unlikely to result in worker exposures exceeding the current ACGIH(R) threshold limit value of 200 ppm. This study also confirmed prior studies suggesting that when a relatively volatile chemical is located within arm's length (near field), breathing zone concentrations will be about two- to threefold greater than the room concentration when the air exchange rate is 5-10 ACH.

Benzene exposures associated with tasks performed on marine vessels (circa 1975 to 2000)

In this article, we assemble and synthesize the available industrial hygiene data that describe exposure during the marine transport of benzene-containing products in the United States and abroad. A total of 25 studies were identified and summarized. The measured airborne concentrations of benzene on marine vessels were found to vary depending on several key factors, including the job task, vessel characteristics, cargo type, and sample type and duration. Despite the differences in sampling strategies and benzene content of the liquids being transported, personal time-weighted-average benzene air concentrations typically ranged from 0.2-2.0 ppm during closed loading and 2-10 ppm during open loading operations. Benzene exposures during these activities are likely due to specific short-term tasks, such as connecting and disconnecting hoses and tank gauging and sampling. Similar concentrations of benzene have been reported in the pump room during marine loading operations and during tank cleaning activities in various settings. When compared with contemporaneous occupational health standards, our review indicates that most activities performed on marine vessels from the 1970s to 1990s usually did not result in benzene exposures that exceeded these standards. The information and data presented here may be useful for quantitatively estimating or reconstructing historical exposures during the marine transport of benzene-containing cargo if details about individual's work histories in the maritime industry are available.

Final report on the safety assessment of ethoxyethanol and ethoxyethanol acetate

Ethoxyethanol is an ether alcohol described as a solvent and viscosity-decreasing agent for use in cosmetics. Ethoxyethanol Acetate is the ester of Ethoxyethanol and acetic acid described as a solvent for use in cosmetics. Although these ingredients have been used in the past, neither ingredient is in current use. Ethoxyethanol is produced by reacting ethylene oxide with ethyl alcohol. Ethoxyethanol Acetate is produced via an esterification of Ethoxyethanol and acetic acid, acetic acid anhydride, or acetic chloride. Ethoxyethanol is metabolized to ethoxyacetaldehyde, which is further metabolized to ethoxyacetic acid, which is also a metabolite of Ethoxyethanol Acetate. Low to moderate acute inhalation toxicity is seen in animals studies. Acute oral toxicity studies in several species reported kidney damage, including extreme tubular degeneration. Kidney damage was also seen in acute dermal toxicity studies in rats and rabbits. Minor liver and kidney damage was also seen in short-term studies of rats injected subcutaneously with Ethoxyethanol, but was absent in dogs dosed intravenously. Mixed toxicity results were also seen in subchronic tests in mice and rats. Ethoxyethanol and Ethoxyethanol Acetate were mild to moderate eye irritants in rabbits; mild skin irritants in rabbits, and nonsensitizing in guinea pigs. Most genotoxicity tests were negative, but chromosome aberrations and sister-chromatid exchanges were among the positive results seen. Numerous reproductive and developmental toxicity studies, across several species, involving various routes of administration, indicate that Ethoxyethanol and Ethoxyethanol Acetate are reproductive toxicants and teratogens. Mild anemia was reported in individuals exposed occupationally to Ethoxyethanol, which resolved when the chemical was not used. Reproductive effects have been noted in males exposed occupationally to Ethoxyethanol. Although there are insufficient data to determine the potential carcinogenic effects of Ethoxyethanol or Ethoxyethanol Acetate, there is evidence that these chemicals are absorbed across human skin and that they are reproductive and developmental toxicants via dermal exposure. Therefore, these ingredients are unsafe for use in cosmetic formulations.

Developmental Toxicity Interactions of Methanol and Radiofrequency Radiation or 2-Methoxyethanol in Rats

This research was undertaken to determine potential interactions among chemical and physical agents. Radiofrequency (RF) radiation is used in numerous workplaces, and many workers are concurrently exposed to RF radiation and various chemicals. The developmental toxicity of RF radiation is associated with the degree and duration of hyperthermia induced by the exposure. Previous animal research indicates that hyperthermia induced by an elevation in ambient temperature can potentiate the toxicity and teratogenicity of some chemical agents. We previously demonstrated that combined exposure to RF radiation (10 MHz) and the industrial solvent, 2-methoxyethanol (2ME), enhanced teratogenicity in rats. Interactions were noted at even the lowest levels of 2ME tested, but only at hyperthermic levels of RF radiation. The purpose of the present research is to investigate if the interactive effects noted for RF radiation and 2ME are unique to these agents, or if similar interactions might be seen with other chemicals. Because methanol is widely used as a solvent as well as fuel additive, and, at high levels, is teratogenic in animals, we selected methanol as a chemical to address generalizability. Based on the literature and our pilot studies, 0, 2, or 3 g/kg methanol (twice, at 6-hour intervals) were administered on gestation day 9 or 13 to groups of 10 Sprague-Dawley rats. Dams treated on day 9 were given methanol and exposed to RF radiation sufficient to maintain colonic temperature at 41°C for 60 minutes (or sham). Those treated on day 13 were given methanol plus either 0 or 100 mg/kg 2ME. Because we observed that methanol produced hypothermia, some groups were given the initial dose of methanol concurrently with the RF or 2ME, and others were given the first dose of methanol 1.5 hours prior to RF or 2ME. Dams were sacrificed on gestation day 20, and the fetuses were examined for external malformations. The results indicate that RF radiation or methanol on day 9 increased the incidence of resorbed fetuses, but no interactive effects were observed. The resorptions were highest in groups given the experimental treatments 1.5 hours apart. The higher dose of methanol also reduced fetal weights. Administration of 2ME or methanol on day 13 increased the rate of malformations, and there was evidence of a positive interaction between 2ME and methanol. Fetal weights were reduced by 2ME and methanol alone, but no interaction was observed. Also, separation of the dosing with the teratogens did not affect the results. These results point out that interactions in developmental toxicology, such as those of RF radiation, 2ME, and methanol that we have studied, are complex, and such interactions cannot be fully understood or predicted without more research. It is important that combined exposure effects be considered when developing both physical agent and chemical agent exposure guidelines and intervention strategies.

Interactions of radiofrequency radiation-induced hyperthermia and 2-methoxyethanol teratogenicity in rats

Radiofrequency (RF) radiation is used in a variety of workplaces. In addition to RF radiation, many workers are concurrently exposed to numerous chemicals; exposed workers include those involved with the microelectronics industry, plastic sealers, and electrosurgical units. The developmental toxicity of RF radiation is associated with the degree and duration of hyperthermia induced by the exposure. Previous animal research indicates that hyperthermia induced by an elevation in ambient temperature can potentiate the toxicity and teratogenicity of some chemical agents. We previously demonstrated that combined exposure to RF radiation (10 MHz) and the industrial solvent, 2-methoxyethanol (2ME), produces enhanced teratogenicity in rats. The purpose of the present research is to determine the effects of varying the degree and duration of hyperthermia induced by RF radiation (sufficient to maintain colonic temperatures at control [38.5], 39.0, 40.0, or 41.0 degrees C for up to 6 h) and 2ME (100 mg/kg) administered on gestation day 13 of rats. Focusing on characterizing the dose-response pattern of interactions, this research seeks to determine the lowest interactive effect level. Day 20 fetuses were examined for external and skeletal malformations. The results are consistent with previous observations. Significant interactions were observed between 2ME and RF radiation sufficient to maintain colonic temperatures at 41 degrees C for 1 h, but no consistent interactions were seen at lower temperatures even with longer durations. These data indicate that combined exposure effects should be considered when developing both RF radiation and chemical exposure guidelines and intervention strategies.

A toxicokinetic study of inhaled ethylene glycol monomethyl ether (2-ME) and validation of a physiologically based pharmacokinetic model for the pregnant rat and human

Exposures to sufficiently high doses of ethylene glycol monomethyl ether (2-methoxyethanol, 2-ME) have been found to produce developmental effects in rodents and nonhuman primates. The acetic acid metabolite of 2-ME, 2-methoxyacetic acid (2-MAA), is the likely toxicant, and, as such, an understanding of the kinetics of 2-MAA is important when assessing the potential risks to humans associated with 2-ME. A previously described physiologically based pharmacokinetic (PBPK) model of 2-ME/2-MAA kinetics for rats exposed via oral or iv administration was extended and validated to inhalation exposures. Pregnant Sprague-Dawley rats were exposed for 5 days (gestation days 11-15), 6 h/day, to 2-ME vapor at 10 and 50 ppm. Validation consisted of comparing model output to maternal blood and fetal 2-ME and 2-MAA concentrations during and following 5 days of exposure (gestation days 11-15). These concentrations correspond to a known no observed effect level (NOEL) and a lowest observed effect level (LOEL) for developmental effects in rats. The rat PBPK model for 2-ME/2-MAA was scaled to humans and the model (without the pregnancy component) was used to predict data collected by other investigators on the kinetics of 2-MAA excretion in urine following exposures to 2-ME in human volunteers. The partially validated human model (with the pregnancy component) was used to predict equivalent human exposure concentrations based on 2-MAA dose measures (maximum blood concentration, C(max), and average daily area under the 2-MAA blood concentration curve, AUC, during pregnancy) that correspond to the concentrations measured at the rat NOEL and LOEL exposure concentrations. Using traditional PBPK scale-up techniques, it was calculated that pregnant women exposed for 8 h/day, 5 days/week, for the duration of pregnancy would need to be exposed to 12 or 60 ppm 2-ME to produce maternal 2-MAA blood concentrations (C(max) or average daily AUC) equivalent to those in rats exposed to the NOEL (10 ppm) or LOEL (50 ppm), respectively.

A toxicokinetic study of inhaled ethylene glycol ethyl ether acetate and validation of a physiologically based pharmacokinetic model for rat and human

The solvents ethylene glycol monoethyl ether acetate (EGEEA) and ethylene glycol monoethyl ether (EGEE), at sufficiently high doses, are known to be rodent developmental toxicants, exerting their toxic effects through the action of their metabolite 2-ethoxyacetic acid (2-EAA). Thus risks associated with exposure to these compounds are best evaluated based on a measure of the internal dose of 2-EAA. The goals of the work reported here were to develop physiologically based pharmacokinetic (PBPK) models of EGEEA and EGEE for pregnant rats and humans. These models were used to identify human exposure levels (ppm in air) equivalent to the rat no observed effect level (NOEL) and lowest observed effect level (LOEL) for developmental effects (Hanley et al., 1984). We exposed pregnant Sprague-Dawley rats to concentrations of EGEEA corresponding to the NOEL and LOEL. Maternal blood, urine, and fetal tissue concentrations of EGEE and 2-EAA measured in these experiments were used to validate the rat EGEEA and EGEE models. Data collected by other researchers were used to validate the capabilities of the rodent EGEEA and EGEE models to predict the kinetics in humans. The models for estimating circulating blood concentrations of 2-EAA were considered valid based on the ability of the model to accurately predict 2-EAA concentrations in rat blood, urine, and fetal tissue. The human inhaled concentration equivalent to the rat NOEL for EGEEA (50 ppm) was predicted to be 25 ppm using the maternal blood average daily area under the curve (AUC) and 40 ppm using the maximum concentration achieved in maternal blood (C(max)). The human inhaled concentration equivalent to the rat LOEL for EGEEA (100 ppm) was determined to be 55 ppm using the maternal blood average daily AUC and 80 ppm using the maternal blood C(max).

Developmental toxicity interactions of salicylic acid and radiofrequency radiation or 2-methoxyethanol in rats

Radiofrequency (RF) radiation is used in a variety of workplaces where workers are concurrently exposed to chemicals. Combined exposure to RF radiation (10 MHz) and the industrial solvent, 2-methoxyethanol (2ME), produces enhanced teratogenicity in rats. The purpose of the present research was to determine if the synergistic effects noted for RF radiation and 2ME are generalizable to other chemicals. Since salicylic acid (SA) is widely used as an analgesic and is teratogenic in animals, SA was selected to address generalizability. Based on the literature and our pilot studies, 0, 250, or 350 mg/kg SA were administered by gavage on gestation Day 9 or 13 to rats. Concurrently rats given SA on Day 9 were exposed to RF radiation sufficient to maintain colonic temperature at 41 degrees C for 60 min (or sham). Those given SA on Day 13 were also given 0 or 100 mg/kg 2ME (gavage). Dams were sacrificed on gestation Day 20, and the fetuses were examined for external malformations. The data provide no evidence of synergistic interactions between RF radiation and salicylic acid (resorptions and malformations). Limited evidence of antagonism was observed between 2ME and salicylic acid (fetal weights). This investigation highlights the importance of additional research on interactions in developmental toxicology, and emphasizes the need to consider combined exposure effects when developing both physical agent and chemical agent exposure guidelines and intervention strategies.

Proposal for the assessment of quantitative dermal exposure limits in occupational environments: Part 1. Development of a concept to derive a quantitative dermal occupational exposure limit

Dermal uptake of chemicals at the workplace may contribute considerably to the total internal exposure and so needs to be regulated. At present only qualitative warning signs--the "skin notations"--are available as instruments. An attempt was made to develop a quantitative dermal occupational exposure limit (DOEL) complementary to respiratory occupational exposure limits (OELs). The DOEL refers to the total dose deposited on the skin during a working shift. Based on available data and experience a theoretical procedure for the assessment of a DOEL was developed. A DOEL was derived for cyclophosphamide and 4,4-methylene dianiline (MDA) according to this procedure. The DOEL for MDA was tested for applicability in an actual occupational exposure scenario. An integrated approach is recommended for situations in which both dermal and respiratory exposures contribute considerably to the internal exposure of the worker. The starting point should be an internal health based occupational exposure limit--that is, the maximum dose to be absorbed without leading to adverse systemic effects. The proposed assessment of an external DOEL is then either based on absorption rate or absorption percentage. The estimation of skin penetration seems to be of crucial importance in this concept. If for a specific substance a maximal absorption rate can be estimated a maximal skin surface area to be exposed can be assessed which may then serve the purpose of a DOEL. As long as the actual skin surface exposed is smaller than this maximal skin surface area the internal OEL will not be exceeded, and therefore, no systemic health problems would be expected, independent of the dermal dose/unit area. If not, the DOEL may be interpreted as the product of dermal dose/unit area (mg/cm2) and exposed skin surface area (cm2). The proposed concept for a DOEL is relevant and can be made applicable for health surveillance in the occupational situation where dermal exposure contributes notably to the systemic exposure. Further research should show whether this concept is more generally applicable.

Repeated high dose oral exposure or continuous subcutaneous infusion of 2-methoxyacetic acid does not suppress humoral immunity in the mouse

2-Methoxyethanol (ME) has been shown to be immunosuppressive in rats but not mice, with oxidation of ME to 2-methoxyacetic acid (MAA) being a prerequisite for immunosuppression. MAA is more rapidly cleared by mice than rats, consequently this study was designed to determine if increasing the bioavailability of MAA in mice might play a role in this species difference. Female B6C3F1 mice were given MAA by oral multiple daily high doses or by continuous subcutaneous infusion via mini-osmotic pumps. Humoral immunity was evaluated in MAA-exposed mice using the plaque-forming cell (PFC) response to either sheep red blood cells (SRBC) or trinitrophenyl-lipopolysaccharide (TNP-LPS). Female F344 rats were also used to compare the effects of multiple daily MAA exposure on these humoral immune responses. Rats and mice were dosed orally twice a day for 4 days by gavage with MAA at dosages ranging from 40-320 mg/kg/day and 240-1920 mg/kg/day, respectively. All animals were immunized on the first day of dosing and body and lymphoid organ weights and PFC responses to SRBC or TNP-LPS were evaluated 4 days later. While body weights in rats were unaffected, thymus weights were reduced at all dosages of MAA and spleen weights were reduced at 160 or 320 mg/kg/day. PFC responses to SRBC and TNP-LPS were suppressed in rats at dosages of 160 and 320 mg/kg/day. In contrast, thymus weights of mice were reduced only at 960 mg/kg/day or greater, with no effect on spleen or body weights. Furthermore, neither the PFC response to SRBC nor the response to TNP-LPS was suppressed in mice exposed to any oral dosage of MAA. In the continuous infusion study, mice were subcutaneously implanted with mini-osmotic pumps containing MAA which was delivered at 840 mg/kg/day over a 7-day period. Continuous exposure to MAA via mini-osmotic pumps did not suppress the PFC response to either SRBC or TNP-LPS, but rather significantly enhanced the response to TNP-LPS. These results indicate that mice are insensitive to MAA even at the high dosages given as a bolus or continuously over 1 week. The data further support earlier work, which suggested that the observed difference between rats and mice for MAA-induced immunosuppression appears to be unrelated to the availability of MAA to target lymphoid tissue in these rodent species.

Association of spontaneous abortion and other reproductive effects with work in the semiconductor industry

This study tested the hypothesis that fabrication room (fab) work in the silicon-based semiconductor industry is associated with an increased risk of spontaneous abortion (SAB). The study was conducted nationwide at 14 companies representing a spectrum of large to small manufacturers. A small increase in risk of SAB was observed among fab workers compared with nonfabrication room (nonfab) workers in two cohorts, historical (adjusted RR = 1.43, 95% confidence interval [CI] 0.95-2.09) and prospective (adjusted RR = 1.25, 95% CI = 0.63-1.76). Analysis of specific fab exposures in the historical cohort showed a consistent, dose-response association of SAB with photoresist and developer solvents, whose major component was ethylene-based glycol ethers. The consistency of our findings and the toxicological data for these agents suggest that this is a causal association. Independent associations of SAB with self-reported stress and with etching fluorides were observed and require further research. No significant decrease in fertility was observed among men or women working in fabs, but reduced fecundability was suggested for some women fab workers.

Toxicological investigations in the semiconductor industry: III: Studies on prenatal toxicity caused by waste products from aluminum plasma etching processes

The prenatal toxic effects of contaminated vacuum pump oil (Sample A) and solid waste products (Samples B and C) originating from aluminum plasma etching processes in semiconductor manufacturing were investigated. Three strains of pregnant mice with different degrees of sensitivity during organogenesis (days 6-15 of gestation) were treated daily with 1000 mglkg b.w. (Sample A), 500 or 750 mg/kg b.w. (Sample B), and 250, 500, or 750 mg/kg b.w. (Sample C). On day 18 of pregnancy, the animals were killed and examined for gross changes, number and weight of live fetuses, as well as the number of postimplantation losses and malformations. Analytical data showed that the investigated wastes contained various halogenated hydrocarbons and inorganic compounds. Sample A revealed no signs of prenatal toxic action. In contrast, administration of Samples B and C caused strong prenatal toxic effects. The number of live fetuses declined in a dose--related manner, and evidence of intrauterine growth retardation was noted in fetuses that survived to day 18. The number of fetuses with malformations (only cleft palates) rose significantly in accordance with the doses and sensitivity of the strains (> 95 % of the fetuses of the most sensitive strain after 750 mg/kg; 85% after 500 mg/kg).

Interactive developmental toxicity of radiofrequency radiation and 2-methoxyethanol in rats

Concurrent exposures to chemical and physical agents occur in the workplace; exposed workers include those involved with the microelectronics industry, plastic sealers, and electrosurgical units. Previous animal research indicates that hyperthermia induced by an elevation in ambient temperature can potentiate the toxicity and teratogenicity of some chemical agents. We previously demonstrated that combined exposure to radiofrequency (RF; 10 MHz) radiation, which also induces hyperthermia and is teratogenic to exposed animals, and the industrial solvent, 2-methoxyethanol (2ME), produces enhanced teratogenicity in rats. The present study replicates and extends the previous research investigating the enhanced teratogenicity of combined RF radiation and 2ME exposures. The interactive dose-related teratogenicity of RF radiation (sham exposure or maintaining colonic temperatures at 42.0 degrees C for 0, 10, 20, or 30 min) and 2ME (0, 75, 100, 125, or 150 mg/kg) was investigated by administering various combinations of RF radiation and 2ME to groups of rats on gestation days 9 or 13; gestation-day 20 fetuses were examined for external, skeletal, and visceral malformations. The results are consistent with and extend our previous research findings. Synergism was observed between RF radiation and 2ME for some treatment combinations, but not for others. The study also clarified which gestational periods, RF radiation exposure durations, and 2ME doses would be most informative in future interaction studies to determine the lowest interactive effect level. Day 9 exposures generally evidenced little effect by 2ME, either by itself or in combination with RF radiation. In contrast, day 13 exposures resulted in highly significant effects from 2ME and RF radiation. The structures showing strong evidence of effects from both 2ME and RF radiation after exposure on gestation day 13 were the forepaw digits, forepaw phalanges, hindpaw digits, hindpaw phalanges, hind limbs, metacarpals, and metatarsals. Statistical analyses did not show a global synergistic effect, but did show evidence for a synergistic effect at intermediate levels of the dose ranges. Future research will address potential interactions at lower doses.

Species and strain comparisons of immunosuppression by 2-methoxyethanol and 2-methoxyacetic acid

2-Methoxyethanol (ME) and its principal metabolite 2-methoxyacetic acid (MAA) have been shown in our laboratory to be immunosuppressive in male Fischer 344 rats. In this study several strains of 12-week-old female rats and mice were used to compare the immunosuppressive activity of equimolar concentrations of ME and MAA on the trinitrophenyl-lipopolysaccharide (TNP-LPS) antibody plaque-forming cell (PFC) response, which we previously demonstrated to be a sensitive end point. Female inbred Lewis, Fischer 344 and Wistar/Furth, and outbred Sprague-Dawley rats were dosed by gavage with either ME or MAA at dosages of 0.33 to 2.64 mmol/kg/day for 10 consecutive days. Female inbred C3H and C57BL/6J, hybrid B6C3F1, and outbred CD-1 mice were similarly dosed with equimolar dosages of 0.66 to 5.28 mmol/kg/day ME or MAA. All animals were immunized on day 9 of dosing and PFC responses evaluated 3 days later. Suppression of the PFC response was observed in all strains of rats at 2.64 mmol/kg/day ME or MAA. Lewis and Wistar/Furth rats were found to be the most sensitive strains with suppression at levels as low as 0.66 mmol/kg/day ME or MAA. While ME and MAA dosing resulted in suppression of the TNP PFC response in all the rat strains tested, such treatment did not suppress this PFC response in any of the mouse strains examined. These results indicate that under the conditions of this study rats, but not mice, are immunosuppressed by ME and MAA exposure, and that the susceptibility to immunosuppression differs among rat strains.

Differences between rats and mice in the immunosuppressive activity of 2-methoxyethanol and 2-methoxyacetic acid

Previous studies from this laboratory have demonstrated that 2-methoxyethanol (ME) and its principal metabolite 2-methoxyacetic acid (MAA) are immunosuppressive in young adult male Fischer 344 rats. In the present study, the immunosuppressive potential of ME and MAA was evaluated in young adult female Fischer 344 rats and C57BL/6J mice. Rats and mice were dosed by gavage with either ME or MAA in water, at dosages ranging from 50-400 mg/kg/day, for 10 consecutive days. Rats and mice were examined for alterations in body, spleen and thymus weights and mitogen-induced proliferation of splenic lymphocytes in vitro; separate groups were employed for the antibody plaque-forming cell (PFC) response to trinitrophenyl-lipopolysaccharide (TNP-LPS). Rats dosed at 100-400 mg/kg/day ME and rats dosed at 50-400 mg/kg/day MAA had decreased thymus weights in the absence of decreased body or spleen weights. Lymphoproliferative (LP) responses to concanavalin A (Con A), phytohemagglutinin (PHA), pokeweed mitogen (PWM) and Salmonella typhimurium mitogen (STM) were all reduced in rats treated with all dosages of ME. Rats treated with MAA displayed similar reductions in these LP responses except that the responses to PWM and STM in rats dosed at 50 mg/kg/day were not reduced. In contrast to the effects of ME and MAA on these end points in the rat, no thymic involution or suppression of LP responses were observed in mice dosed at 50-400 mg/kg/day. The PFC response to TNP-LPS was suppressed in rats dosed with either ME or MAA at dosages of 100-400 mg/kg/day. ME and MAA, however, failed to suppress the PFC response in mice immunized with TNP-LPS. These results indicate that unlike Fischer 344 rats, C57BL/6J mice are insensitive to the immunosuppressive effects of ME and MAA at the dosages employed in this study. Whether the different sensitivities of these two rodent species to ME- and MAA-induced immunosuppression are due to immunologic, pharmacokinetic or metabolic differences within each species remains to be determined.

Evaluation of 2-methoxyacetic acid toxicity on mouse germ cells by flow cytometry

Flow cytometric (FCM) DNA content measurements were carried out on testicular monocellular suspensions obtained from mice exposed per os to a single dose of 50, 100, 300, 600, and 900 mg/kg body weight (b.w.) of 2-methoxyacetic acid (MAA) in order to investigate its cytotoxic action on germ cells. The effects of MAA were evaluated 2, 7, 14, 28, and 45 d after treatment in terms of altered cell type ratios in FCM fluorescence distribution histograms. Testis weight and histological tissue sections were also analyzed. MAA induced marked changes in the relative percentages of tetraploid and haploid cells, indicating the occurrence of cytotoxic damage on primary spermatocytes. Multiparameter FCM analysis showed that, besides its action on nucleic acid synthesis, MAA can also affect the cellular energy metabolism reflected in an altered mitochondrial mass distribution on round spermatids surviving the MAA treatment. This study demonstrates that rapid and unique FCM procedures can be usefully applied in reproductive toxicology.

Important recent advances in the practice of health risk assessment: implications for the 1990s

Health risk assessments have been so widely adopted in the United States that their conclusions are a major factor in many environmental decisions. The procedure by which these assessments are conducted is one which has evolved over the past 10-15 years and a number of short-comings have been widely recognized. Unfortunately, improvements in the process have often occurred more slowly than advancements in technology or scientific knowledge. Recent significant advances for more accurately estimating the risks posed by environmental chemicals are likely to have a dramatic effect on the regulation of many substances. Each of the four portions of risk assessment (hazard identification, dose-response assessment, exposure assessment, and risk characterization) has undergone significant refinement since 1985. This paper reviews some of the specific changes and explains the likely benefits as well as the implications. Emphasis is placed on the improved techniques for (a) identifying those chemicals which may pose a human cancer or developmental hazard, (b) using statistical approaches which account for the distribution of interindividual biological differences, (c) using lognormal statistics when interpreting environmental data, (d) using physiologically based pharmacokinetic models for estimating delivered dose and for scaling up rodent data, (e) using biologically based cancer models to account for the seven or more apparently different mechanisms of chemical carcinogenesis, (f) describing the severity of the public health risks by considering those portions of the population exposed to various concentrations of a contaminant, and (g) reviewing how criteria for acceptable risk have been influenced by the number of exposed persons. The net benefit of these improvements should be a reduction in the uncertainty inherent in current estimates of the health risks posed by low level exposure to carcinogens and developmental toxicants.