An Assessment of the Carcinogenic Potential of Trichloroethylene in Humans

Controversy surrounds the assessments of carcinogenic potential associated with human exposure to trichloroethylene (TCE). The American Conference of Governmental Industrial Hygienists states that TCE is “not suspected to be a human carcinogen.” In contrast, the International Agency for Research on Cancer has classified TCE as a probable human carcinogen, based primarily on the results of animal toxicity studies. Chronic high-dose TCE exposures cause hepatic and pulmonary tumors in mice and renal tumors in rats. Human epidemiology studies, however, do not support a causal association between exposure to TCE at environmentally relevant levels and cancers of the lung, liver, or kidney. The apparent discrepancy between the animal data and the human data can be explained by (1) differences in TCE exposure levels between laboratory animals and humans, (2) species-specific differences in TCE metabolism, and (3) other species-specific mechanisms involved in the development of cancer in rodents. This paper critically assesses the experimental and epidemiological data relevant to the carcinogenic potential of TCE. From the analysis, we conclude that TCE exposure at concentrations likely to be encountered in most environmental media is not likely to cause liver, lung, or kidney cancers in humans.     

Assaying the Effect of Levodopa on the Evaluation of Risk in Healthy Humans

In humans, dopamine is implicated in reward and risk-based decision-making. However, the specific effects of dopamine augmentation on risk evaluation are unclear. Here we sought to measure the effect of 100 mg oral levodopa, which enhances synaptic release of dopamine, on choice behaviour in healthy humans. We use a paradigm without feedback or learning, which solely isolates effects on risk evaluation. We present two studies (n = 20; n = 20) employing a randomised, placebo-controlled, within-subjects design. We manipulated different dimensions of risk in a controlled economic paradigm. We test effects on risk-reward tradeoffs, assaying both aversion to variance (the spread of possible outcomes) and preference for relative losses and gains (asymmetry of outcomes - skewness), dissociating this from potential non-specific effects on choice randomness using behavioural modelling. There were no systematic effects of levodopa on risk attitudes, either for variance or skewness. However, there was a drift towards more risk-averse behaviour over time, indicating that this paradigm was sensitive to detect changes in risk-preferences. These findings suggest that levodopa administration does not change the evaluation of risk. One possible reason is that dopaminergic influences on decision making may be due to changing the response to reward feedback.     

A Fuzzy Logic Approach to Assess,Manage, and Communicate Carcinogenic Risk

A prospective approach to addressing carcinogen risk assessment is presented. Fuzzy reasoning is used to assess carcinogenic risk, characterize it, and control it. The approach is inspired by fuzzy control inference that deploys linguistic intelligence as input to a system described numerically through membership functions. Fuzzy-based reasoning to estimate carcinogenic risk provides several advantages as discussed here. The fuzzy reasoning approach has more capabilities than traditional models in dealing with risk agents that are probably carcinogens, possibly carcinogens, not classifiable as carcinogens, and probably not carcinogens. Input–output surfaces are presented for each hazard group to enable fast inferencing. Then, a hypothetical example is given to compare the results of traditional methods and the fuzzy-based approach to estimating the risk of a carcinogen to a human population. Results show similarity in risk characterization with less input information to the fuzzy-based approach. Fuzzy reasoning characterizes risk in more explicit and easy to grasp terms. Two outputs of the inferencing system are risk characterization and risk control or remediation.     

Investigating the Contribution of Peri-domestic Transmission to Risk of Zoonotic Malaria Infection in Humans

BackgroundIn recent years, the primate malaria Plasmodium knowlesi has emerged in human populations throughout South East Asia, with the largest hotspot being in Sabah, Malaysian Borneo. Control efforts are hindered by limited knowledge of where and when people get exposed to mosquito vectors. It is assumed that exposure occurs primarily when people are working in forest areas, but the role of other potential exposure routes (including domestic or peri-domestic transmission) has not been thoroughly investigated.Conclusions/SignificanceThis study shows there is a possibility that humans can be exposed to P. knowlesi infection around their homes. The vector is highly exophagic and few were caught indoors indicating interventions using bednets inside households may have relatively little impact.     

Mapping Risk of Nipah Virus Transmission from Bats to Humans in Thailand

Nipah virus (NiV) is a zoonotic virus that can pose a serious threat to human and livestock health. Old-world fruit bats (Pteropus spp.) are the natural reservoir hosts for NiV, and Pteropus lylei, Lyle’s flying fox, is an important host of NiV in mainland Southeast Asia. NiV can be transmitted from bats to humans directly via bat-contaminated foods (i.e., date palm sap or fruit) or indirectly via livestock or other intermediate animal hosts. Here we construct risk maps for NiV spillover and transmission by combining ecological niche models for the P. lylei bat reservoir with other spatial data related to direct or indirect NiV transmission (livestock density, foodborne sources including fruit production, and human population). We predict the current and future (2050 and 2070) distribution of P. lylei across Thailand, Cambodia, and Vietnam. Our best-fit model predicted that central and western regions of Thailand and small areas in Cambodia are currently the most suitable habitats for P. lylei. However, due to climate change, the species range is predicted to expand to include lower northern, northeastern, eastern, and upper southern Thailand and almost all of Cambodia and lower southern Vietnam. This expansion will create additional risk areas for human infection from P. lylei in Thailand. Our combined predictive risk maps showed that central Thailand, inhabited by 2.3 million people, is considered highly suitable for the zoonotic transmission of NiV from P. lylei. These current and future NiV transmission risk maps can be used to prioritize sites for active virus surveillance and developing awareness and prevention programs to reduce the risk of NiV spillover and spread in Thailand.

     

Trends in Risk Assessment of Chemicals in the European Union

Current legislation in the European Union (EU) requires a risk assessment for industrial chemicals. The underlying procedures and paradigms of such EU risk assessment for new and existing chemicals are explained. The risk assessment is performed according to a harmonised methodology, laid down in the Technical Guidance Documents (TGD). Important new, technical risk assessment aspects covered in a recent revision round of the TGD are highlighted. The most prominent change in the environmental TGD part is the addition of the marine risk assessment, including a Persistent Bioaccumulation and Toxicity (PBT) assessment. In the human health part a significant change is the new data requirement for reproductive toxicity. The performance of both the risk assessment and the risk reduction phase of EU existing chemicals have been evaluated. An important conclusion was that our a priori knowledge on possible risks of chemicals is poor. The European Commission has recently launched a proposal (REACH) for drastically changing the risk management process of industrial chemicals in the EU. Major changes are a shift in responsibility from authorities to industry (including downstream users) for the safe use of chemicals, an acceleration of data collection for ‘non-assessed’ chemicals, and an authorization step for substances of very high concern.     

A Simple Bioassay for Chemicals Active to the Photosynthetic or Respiratory Systems of Plants

After male rats of the Sprague Dawley strain, 5 weeks old, were fed a 20% casein diet with or without 0.5% nicotinamide for 13 days, 180 mg/kg body weight of alloxan was injected in- traperitoneally into the rats. The rats were kept for 18 days with the same diet. The level of blood glucose was increased 6-fold in the group on a 20% casein diet by the injection of alloxan, while there was only a 2-foid increase in the group on a nicotinamide-containing diet and the decreased body weight was also lower in the group on the nicotinamide diet than the group on the casein diet. The body weight was indirectly related to the concentration of blood glucose. A marked increase was observed in the activities of tryptophan oxygenase, aminocarboxymuconate-semialdehyde decarboxylase, and nicotinamide methyltransferase upon the injection of alloxan with both diets; on the other hand, the activities of kynureninase and NAD⁺ synthetase were decreased by the injection of alloxan. The activity of kynurenine aminotransferase increased in the group on the 20% casein diet by the injection of alloxan, while in the group on the nicotinamide-containing diet its activity was not increased by the injection. These changes in the above enzyme activities mean that the conversion ratio from tryptophan to niacin is lower in the alloxan diabetic rat than normal rat. It was found that the activities of tryptophan oxygenase, aminocarboxymuconate-semialdehyde decarboxylase, and nicotinamide methyltransferase were directly related to the concentration of blood glucose, and that the activities of kynureninase and NAD⁺ synthetase were inversely related. There was no difference in the activities of 3-hydroxyanthranilic acid oxygenase and nicotinamide mononucleotide adenylyltransferase upon the injection of alloxan with both diets.     

Incorporating Information on Bioavailability of Soil-Borne Chemicals into Human Health Risk Assessments

Definition of the term bioavailability varies in the environmental sciences. In human health risk assessment, bioavailability is defined as the fraction of the dose of chemical delivered that is absorbed into the systemic circulation. Bioavailability can be expressed as either absolute or relative bioavailability, and both are important in calculating risks from contaminants in soils. Bioavailability of chemicals is addressed in all risk assessments, although not always in a transparent manner. Because data on bioavailability are limited, approximations and assumptions regarding chemical uptake are extensively used. The risk assessment process could benefit from new information on the bioavailability of chemicals, but there are important questions about the best means to develop this information and how it should be used. To foster discussion on these issues, three articles are presented in this issue of the journal offering different perspectives on bioavailability method development, validation, and use.     

5种药剂对红火蚁的田间药效评价

以活动蚁巢减退率和工蚁减退率为指标,评价红火蚁克星（Ⅳ型）、灭蚁威、火蚁净、蚁净安和灭蚁蝗等5种药剂对红火蚁的防治效果。结果表明,不同药剂间防治效果存在差异,其中药后21 d,红火蚁克星（Ⅳ型）和灭蚁威饵剂均具有很好的防治效果,对蚁巢防效和活动工蚁的防治效果均达90.0%以上。建议采用上述两种药剂进行轮换使用,从而延缓红火蚁产生抗药性。