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W Farland

Publications and source records attributed to W Farland.

8 recordsLinked to original sources
PubMed2000

Current risk assessment approaches in different countries.

Polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs) and biphenyls (PCBs) exist as complex mixtures in environmental and biological samples. There is sufficient evidence that the toxic congeners share a common mode of action, involving binding to the Ah-receptor. Toxic equivalency factors (TEFs) and chemical residue data are used to calculate toxic equivalent (TEQ) concentrations in environmental samples, foods, animal and human tissues. Two different approaches have been used in the risk assessments of PCDDs, PCDFs and dioxin-like PCBs. WHO and most countries outside the USA have derived Tolerable Daily (or weekly) Intakes (TDI) in the order of 1-10 pg per kg of body weight for TCDD or TEQs based on data from rodent carcinogenicity studies. These countries have assumed the existence of a threshold dose for the carcinogenicity of dioxins, while US EPA and USFDA have used probabilistic estimates of cancer potency, treating cancer as a non-threshold effect and using a descriptor that addresses upper bound risk, the Risk Specific Dose (RsD). In the USA and other countries there is a growing concern over the non-cancer effects of dioxin-like compounds. In general, the various risk assessments have identified groups of the population that are at particular high risks and all have stressed the urgent need to reduce the sources of the environmental contamination with these compounds to the lowest possible.

Benzofurans↗
PubMed1997

Implementation of EPA Revised Cancer Assessment Guidelines: Incorporation of Mechanistic and Pharmacokinetic Data.

A workshop entitled "Implementation of EPA Revised Cancer Assessment Guidelines: Incorporation of Mechanistic and Pharmacokinetic Data" was held in Anaheim, California, in 1996 at the 35th Annual Meeting of the Society of Toxicology (SOT). This workshop was jointly sponsored by the Carcinogenesis, Risk Assessment, and Veterinary Specialty Sections of the SOT. The thrust of the workshop was to discuss the scientific basis for the revisions to the EPA Guidelines for cancer assessment and EPA's plans for their implementation. This is the first revision to the original EPA guidelines which have been in use by EPA since 1986. The principal revisions are intended to provide a framework for an increased ability to incorporate biological data into the risk assessment process. Two cases were presented, for chloroform and triclioroethylene, that demonstrated the use of the revised guidelines for specific cancer risk assessments. Using these new guidelines, nonlinear margin of exposure analyses were proposed for these chemicals instead of the linearized multistage model previously used by the EPA as the default method. The workshop participants generally applauded the planned revisions to the EPA guidelines. For the most part, they considered that the revised guidelines represented a positive step which should allow for and encourage the use of biological information in the conduct of cancer risk assessments. Several participants cautioned however that the major problem with cancer risk assessments would continue to be the inadequacy of available data on which to conduct more scientific risk assessments.

Animals↗
PubMed1989

Overview of a workshop on quantitative models for developmental toxicity risk assessment.

A workshop was held to discuss potential advancements to improve the precision of risk estimates for developmental toxicity. This paper presents an overview of the discussions at the workshop, focusing on the risk assessment process and science policy considerations important in the use of quantitative models. Some of the pertinent biological considerations are reviewed, particularly those related to the repair capacity of the developing organism and how this affects the concept of a threshold for developmental toxicity effects, as well as the maternal and litter influences on developmental toxicity outcomes. Finally, the current status of use of quantitative approaches is described, possible short-term approaches are discussed, and future research needs in this area are outlined.

Abnormalities, Drug-Induced↗
PubMedDate not supplied

Dioxins: WHO's tolerable daily intake (TDI) revisited.

In December 1990, the World Health Organization (WHO) established a tolerable daily intake (TDI) of 10 pg/kg b.w. (body weight) for TCDD, based on liver toxicity, reproductive effects and immunotoxicity in experimental animals, and making use of kinetic data in humans and experimental animals. Since then new epidemiological and toxicological data have emerged, in particular with respect to neurodevelopmental and endocrine effects of dioxin. Therefore, the European Centre for Environment and Health of the World Health Organization (WHO-ECEH) and the International Programme on Chemical Safety (IPCS) jointly organized a consultation on the "Assessment of the health risk of dioxins: re-evaluation of the TDI", May 1998, Geneva, Switzerland. The participants discussed the health risks for infants, cancer and non-cancer endpoints in humans and animals, mechanistic aspects, kinetic behaviour, modelling, exposure, and the applicability of the toxic equivalency (TEQ) concept. For the health risk assessment of dioxin-like compounds, the WHO Consultation focused on the most sensitive effects that are considered adverse (hormonal, reproductive and developmental effects) seen at low doses in animal studies (rats and monkeys). Human daily intakes corresponding with body burdens similar to those associated with adverse effects in animals could be estimated to be in the range of 14-37 pg/kg b.w./day. To arrive at a TDI expressed as TEQ, a composite uncertainty factor of 10 was recommended. By applying this uncertainty factor a TDI range of 1-4 pg TEQs/kg body weight was established. An extensive executive summary of the results of this WHO Consultation with all the underlying background documents will be published in Food Additives and Contaminants (in press).

Animals↗