Regulatory cancer risk assessment based on a quick estimate of a benchmark dose derived from the maximum tolerated dose

Human daily dietary intakes of antibiotic residues: Dominant sources and health risks

Antibiotic use in crops is an emerging concern, however, human exposure to antibiotics residues through consumption of plant-derived food has generally been neglected. This study is a comprehensive evaluation based on full consideration of exposure sources and analysis for nearly 100 antibiotics. A total of 58 antibiotic compounds were detected in drinking water (n = 66) and 49 in food samples (n = 150) from Shenzhen, China. The probable daily intake from drinking water and food consumption based on the total concentration of all the detected antibiotic compounds was 310, 200, and 130 ng/kg-body weight/day for preschool children, adolescents, and adults, with a maximum of up to 1400, 970 and 530 ng/kg-bw/day, respectively. Consumption of plant-derived food products, rather than animal-derived food, was the main source of the daily intake, and drinking water was a minor source. Risk assessment suggested a potentially unacceptable health risk from daily intake of norfloxacin, lincomycin and ciprofloxacin. Further research is warranted to alleviate food safety concerns related to antibiotic residues in plant-derived and animal-derived food products.

Efficient detection and assessment of human exposure to trace antibiotic residues in drinking water

Human exposure to antibiotic residues in drinking water has not been well evaluated. This study is the first attempt to simultaneously and efficiently identify and quantify 92 antibiotic residues in filtered tap water (multistage filtration at the tap) (n = 36) collected from 10 areas of a large city in southern China, 10 Chinese brands of bottled/barreled water (n = 30) and six foreign brands of bottled water (n = 18) obtained from the Chinese market. The average and median concentrations of all the detected antibiotic compounds was 182 and 92 ng/L in filtered tap water, 180 and 105 ng/L in Chinese brands of bottled/barreled water, and 666 and 146 ng/L in foreign brands of bottled water, respectively. A total of 58 antibiotics were detected in the filtered tap water, and 45 and 36 antibiotics were detected in the Chinese and foreign brands of bottled water, respectively. More types of antibiotics were detected in Chinese brands of bottled water than in the other bottled waters. In addition, Chinese waters had high roxithromycin concentrations, while the foreign brands of bottled water had high concentrations of dicloxacillin. The average and median values of the estimated overall daily intake of all the detected antibiotics were 4.3 and 2.3 ng/kg/day when only filtered tap water was drunk, 4.0 and 2.5 ng/kg/day when Chinese brands of bottled water was drunk, and 16.0 and 4.9 ng/kg/day when foreign brands of bottled water was drunk. Further study is needed to develop a more comprehensive estimation of human exposure to antibiotic residues in the environment and a more in-depth understanding of the potential hazard of ingested antibiotic residues to the human microbiome.

Human health risk assessment of pharmaceuticals in treated wastewater reused for non-potable applications in Sharjah, United Arab Emirates

Pharmaceuticals and personal care products are an integral part of societal health yet their presence in various environmental compartments, including treated wastewaters, has sparked concerns towards possible human and ecological health effects. The current study aims to characterize human health risks posed by ten pharmaceuticals quantified in wastewater treatment plant effluents where water is reused mainly for landscape irrigation. Receptors were identified as children playing in green areas, adult landscape workers, and adult users of athletic and golf courses irrigated by treated wastewater. The human health risk assessment model exhibited safe exposure (RQ < 1) to all pharmaceuticals for all receptors through both dermal and ingestion exposure pathways. RQs were highest for the landscape worker followed by children playing in green areas and then adult using the athletic fields. RQs were highest to lowest in the following order of pharmaceuticals: acetaminophen, metoprolol, ciprofloxacin, erythromycin, ofloxacin, sulfadiazine, sulfamethoxazole, sulfapyridine, risperidone, and sulfamethazine. Such risk assessment findings aid in supporting decisions to optimize wastewater treatment and reuse strategies, as well as safeguard public and environmental health.

Hormesis: how it could affect the risk assessment process

If the hormetic dose-response were accepted as the default dose-response model for risk assessment it could have important implications for environmental exposure standards for noncarcinogens and especially for carcinogens. Most notably it would lead to the recognition that carcinogens act via a threshold process rejecting the concept of linearity at low doses. The hormetic concept also provides agencies with a broader range of toxicologically-based exposure options, which permit a consideration for avoiding harm, as well as possibly enhancing benefits for both normal and high risk segments of the population. By dismissing hormesis, regulatory agencies such as EPA deny the public the opportunity for optimal health and avoidance of disease.

Screening and human health risk assessment of pharmaceuticals and their transformation products in Dutch surface waters and drinking water

Numerous studies describe the presence of pharmaceuticals in the water cycle, while their transformation products are usually not included. In the current study 17 common pharmaceuticals and 9 transformation products were monitored in the Dutch waters, including surface waters, pre-treated surface waters, river bank filtrates, two groundwater samples affected by surface water and drinking waters. In these samples, 12 pharmaceuticals and 7 transformation products were present. Concentrations were generally highest in surface waters, intermediate in treated surface waters and river bank filtrates and lowest or not detected in produced drinking water. However, the concentrations of phenazone and its environmental transformation product AMPH were significantly higher in river bank filtrates, which is likely due to historical contamination. Fairly constant ratios were observed between concentrations of transformation products and parent pharmaceuticals. This might enable prediction of concentrations of transformation products from concentrations of parent pharmaceuticals. The toxicological relevance of the observed pharmaceuticals and transformation products was assessed by deriving (i) a substance specific provisional guideline value (pGLV) and (ii) a group pGLV for groups of related compounds were under the assumption of additivity of effects within each group. A substantial margin exists between the maximum summed concentrations of these compounds present in different water types and the derived (group) pGLVs. Based on the results of this limited screening campaign no adverse health effects of the studied compounds are expected in (sources of) drinking water in the Netherlands. The presence of transformation products with similar pharmacological activities and concentration levels as their parents illustrates the relevance of monitoring transformation products, and including these in risk assessment. More thorough monitoring yielding information on statistical uncertainty and variability in time and space, and research on possible synergistic effects of low concentration mixtures of compounds belonging to similar pharmacological classes require attention.

Generic Hockey-Stick Model for Estimating Benchmark Dose and Potency: Performance Relative to BMDS and Application to Anthraquinone

Benchmark Dose Model software (BMDS), developed by the U.S. Environmental Protection Agency, involves a growing suite of models and decision rules now widely applied to assess noncancer and cancer risk, yet its statistical performance has never been examined systematically. As typically applied, BMDS also ignores the possibility of reduced risk at low doses ("hormesis"). A simpler, proposed Generic Hockey-Stick (GHS) model also estimates benchmark dose and potency, and additionally characterizes and tests objectively for hormetic trend. Using 100 simulated dichotomous-data sets (5 dose groups, 50 animals/group), sampled from each of seven risk functions, GHS estimators performed about as well or better than BMDS estimators, and a surprising observation was that BMDS mis-specified all of six non-hormetic sampled risk functions most or all of the time. When applied to data on rodent tumors induced by the genotoxic chemical carcinogen anthraquinone (AQ), the GHS model yielded significantly negative estimates of net potency exhibited by the combined rodent data, suggesting that-consistent with the anti-leukemogenic properties of AQ and structurally similar quinones-environmental AQ exposures do not likely increase net cancer risk. In addition to its simplicity and flexibility, the GHS approach offers a unified, consistent approach to quantifying environmental chemical risk.

Toxicological relevance of pharmaceuticals in drinking water

Interest in the public health significance of trace levels of pharmaceuticals in potable water is increasing, particularly with regard to the effects of long-term, low-dose exposures. To assess health risks and establish target concentrations for water treatment, human health risk-based screening levels for 15 pharmaceutically active ingredients and four metabolites were compared to concentrations detected at 19 drinking water treatment plants across the United States. Compounds were selected based on rate of use, likelihood of occurrence, and potential for toxicity. Screening levels were established based on animal toxicity data and adverse effects at therapeutic doses, focusing largely on reproductive and developmental toxicity and carcinogenicity. Calculated drinking water equivalent levels (DWELs) ranged from 0.49 microg/L (risperidone) to 20,000 microg/L (naproxen). None of the 10 detected compounds exceeded their DWEL. Ratios of DWELs to maximum detected concentrations ranged from 110 (phenytoin) to 6,000,000 (sulfamethoxazole). Based on this evaluation, adverse health effects from targeted pharmaceuticals occurring in U.S. drinking water are not expected.

Approaches to the risk assessment of genotoxic carcinogens in food: A critical appraisal

The present paper examines the particular difficulties presented by low levels of food-borne DNA-reactive genotoxic carcinogens, some of which may be difficult to eliminate completely from the diet, and proposes a structured approach for the evaluation of such compounds. While the ALARA approach is widely applicable to all substances in food that are both carcinogenic and genotoxic, it does not take carcinogenic potency into account and, therefore, does not permit prioritisation based on potential risk or concern. In the absence of carcinogenicity dose-response data, an assessment based on comparison with an appropriate threshold of toxicological concern may be possible. When carcinogenicity data from animal bioassays are available, a useful analysis is achieved by the calculation of margins of exposure (MOEs), which can be used to compare animal potency data with human exposure scenarios. Two reference points on the dose-response relationship that can be used for MOE calculation were examined; the T25 value, which is derived from linear extrapolation, and the BMDL10, which is derived from mathematical modelling of the dose-response data. The above approaches were applied to selected food-borne genotoxic carcinogens. The proposed approach is applicable to all substances in food that are DNA-reactive genotoxic carcinogens and enables the formulation of appropriate semi-quantitative advice to risk managers.

Ten challenges for improved ecotoxicological testing in environmental risk assessment

New regulations, in particular the new European chemicals legislation (REACH), will increase the demands on environmental risk assessment (ERA). The requirements on efficient ecotoxicological testing systems are summarized, and 10 major issues for the improvement of ERA practices are discussed, namely: (1) the choice of representative test species, (2) the development of test systems that are relevant for ecosystems in different parts of the world, (3) the inclusion of sensitive life stages in test systems, (4) the inclusion of endpoints on genetic variation in populations, (5) using mechanistic understanding of toxic effects to develop more informative and efficient test systems, (6) studying disruption in invertebrate endocrine mechanisms, that may differ radically from those we know from vertebrates, (7) developing standardized methodologies for testing of poorly water-soluble substances, (8) taking ethical considerations into account, in particular by reducing the use of vertebrates in ecotoxicological tests, (9) using a systematic (statistical) approach in combination with mechanistic knowledge to combine tests efficiently into testing systems, and (10) developing ERA so that it provides the information needed for precautionary decision-making.

Are tumor incidence rates from chronic bioassays telling us what we need to know about carcinogens?

Chronic bioassays for over 500 chemicals have been conducted under the auspices of the National Cancer Institute and/or the National Toxicology Program (NTP) to screen chemicals for carcinogenicity, providing a wealth of information about bioassays. Typically, chemicals are administered for two years to both sexes in each of one strain of rats and mice generally at the maximum tolerated dose (MTD), MTD/2, MTD/4 (in recent years), as well as unexposed control animals. In an attempt to ascertain the sensitivity of this bioassay to detect animal carcinogens tested at the MTD for the current experimental design, the false negative rate (failure to detect increased tumor rates) was investigated. This was accomplished by examining the tumor incidences from over 150 NTP bioassays and estimating the probability that a statistically significant (P0.01) dose-response trend would be obtained at one or more tissue sites in either sex of rats or mice if 200, rather than 50, animals were used per dose group. This provides an estimate of the proportion of chemicals that were not declared high-dose animal carcinogens due to the limited sample size of 50 animals per species-sex-dose group. In this series of chemicals tested, 97/156 (62%) were identified by the NTP to show some or clear evidence of carcinogenicity. With an increase of the number of animals per dose group from 50 to 200, it is estimated that 92% of these chemicals would show statistically significant (P0.01) dose-response trends at one or more tissue sites in either sex of rats or mice. Many of these chemicals are not genotoxic. Some chemicals had no structural alerts for carcinogenicity, but were tested because of potentially high human exposure. This analysis suggests that almost all of the chemicals selected would produce a statistically significant increase in tumor incidence at the MTD with larger sample sizes. Hence, this MTD bioassay screen is not distinguishing between true carcinogens and non-carcinogens. Rather, the screen is simply failing to detect the weaker carcinogens at the MTD. More than 30% of chemicals tested failed to detect statistically significant dose-response trends for tumors because of inadequate sample sizes of 50 animals per dose. Presumably, little or no action would have been taken to regulate exposures to these chemicals as potential carcinogens due to lack of a positive test result. This analysis does not suggest that most chemicals are carcinogenic at human exposure levels nor does it suggest that more than 50 animals should be tested per dose group. With an MTD that may produce a difference (up to 10%) in weight gain between treated and control animals, there quite possibly is cytotoxicity at the MTD. Increased carcinogenicity would be expected from increased opportunities for mutagenic activity during regenerative cell replication to compensate for cytotoxicity. Since it appears that almost all chemicals tested adequately at the MTD will demonstrate carcinogenicity, it is tempting to surmise that this is due in large part to one or more nearly universal modes of action, such as, regenerative cell replication at the MTD rather than due to some unique carcinogenic property of a chemical. That is, the current bioassay possibly is just primarily a screen for the more potent cytotoxins at the MTD, rather than a screen specifically for carcinogenicity. This issue should be examined and suggests that cytotoxicity and cell proliferation should be considered in setting the MTD, particularly for non-genotoxic (non-DNA reactive) chemicals. From a public health view, it is prudent to assume that most chemicals could demonstrate increased tumor incidence rates at the MTD in rodents. The current standard NTP bioassay provides sufficient data to estimate a benchmark dose associated with a specified low tumor incidence to be used as a point-of-departure for cancer risk assessments. The question that should be investigated by a bioassay is not whether a chemical is a carcinogen at the MTD, but what is the relationship between dose and cytotoxicity and/or other modes of action that could produce an excess of tumors?

Comparison of cancer risk estimates based on a variety of risk assessment methodologies

The EPA guidelines recommend a benchmark dose as a point of departure (PoD) for low-dose cancer risk assessment. Generally the PoD is the lower 95% confidence limit on the dose estimated to produce an extra lifetime cancer risk of 10% (LTD(10)). Due to the relatively narrow range of doses in two-year bioassays and the limited range of statistically significant tumor incidence rates, the estimate of the LTD(10) is constrained to a relatively narrow range of values. Because of this constraint, simple, quick estimates of the LTD(10) can be readily obtained for hundreds of rodent carcinogens from the Carcinogenic Potency Database (CPDB) of Gold et al. Three estimation procedures for LTD(10) are described, using increasing information from the CPDB: (A) based on only the maximum tolerated dose (the highest dose tested); (B) based on the TD(50); and (C) based on the TD(50) and its lower 99% confidence limit. As expected, results indicate overall similarity of the LTD(10) estimates and the value of using additional information. For Method (C) the estimator based on the [[(TD(50))(0.36) x (LoConf)(0.64)]/6.6] is generally similar to the estimator based on the one-hit model or multistage model LTD(10). This simple estimate of the LTD(10) is applicable for both linear and curved dose responses with high or low background tumor rates, and whether the confidence limits on the TD(50) are wide or tight. The EPA guidelines provide for a margin of exposure approach if data are sufficient to support a nonlinear dose-response. The reference dose for cancer for a nonlinear dose-response curve based on a 10,000-fold uncertainty (safety) factor from the LTD(10), i.e., the LTD(10)/10,000, is mathematically equivalent to the value for a linear extrapolation from the LTD(10) to the dose corresponding to a cancer risk of <10(-5) (LTD(10)/10,000). The cancer risk at <10(-5) obtained by using the q(1)(*) from the multistage model, is similar to LTD(10)/10,000. For a nonlinear case, an uncertainty factor of less than 10,000 is likely to be used, which would result in a higher (less stringent) acceptable exposure level.

New issues in cancer risk assessment

When a nonlinear dose-response at low doses can be justified, an acceptable daily intake for a carcinogen can be obtained by dividing a benchmark dose, associated with a low incidence of tumors in animals, by uncertainty factors to account for animal-to-human extrapolation, human variability, and risk reduction from a low observed adverse-effect level. This approach can utilize mechanistic information to justify smaller uncertainty factors than typical default values of 10. If a nonlinear dose-response cannot be justified, traditional linear extrapolation from the benchmark dose to zero sometimes gives similar results. This suggests a unified risk-assessment procedure based on uncertainty factors. The issue of cross-species extrapolation based on the risk relative to background risks, rather than excess risk, is examined. The relative risk approach reduces the estimates of cancer risk in humans based on common rodent tumors, such as the liver in some strains of mice.

Paracelsus to parascience: the environmental cancer distraction

Entering a new millennium seems a good time to challenge some old ideas, which in our view are implausible, have little supportive evidence, and might best be left behind. In this essay, we summarize a decade of work, raising four issues that involve toxicology, nutrition, public health, and government regulatory policy. (a) Paracelsus or parascience: the dose (trace) makes the poison. Half of all chemicals, whether natural or synthetic, are positive in high-dose rodent cancer tests. These results are unlikely to be relevant at the low doses of human exposure. (b) Even Rachel Carson was made of chemicals: natural vs. synthetic chemicals. Human exposure to naturally occurring rodent carcinogens is ubiquitous, and dwarfs the general public's exposure to synthetic rodent carcinogens. (c) Errors of omission: micronutrient inadequacy is genotoxic. The major causes of cancer (other than smoking) do not involve exogenous carcinogenic chemicals: dietary imbalances, hormonal factors, infection and inflammation, and genetic factors. Insufficiency of many micronutrients, which appears to mimic radiation, is a preventable source of DNA damage. (d) Damage by distraction: regulating low hypothetical risks. Putting huge amounts of money into minuscule hypothetical risks damages public health by diverting resources and distracting the public from major risks.