Biomedical subjects

Paul Whitehouse

Publications and source records attributed to Paul Whitehouse.

9 recordsLinked to original sources

PubMed2006

Bayesian and time-independent species sensitivity distributions for risk assessment of chemicals.

Species sensitivity distributions (SSDs) are increasingly used to analyze toxicity data but have been criticized for a lack of consistency in data inputs, lack of relevance to the real environment, and a lack of transparency in implementation. This paper shows how the Bayesian approach addresses concerns arising from frequentist SSD estimation. Bayesian methodologies are used to estimate SSDs and compare results obtained with time-dependent (LC50) and time-independent (predicted no observed effect concentration) endpoints for the insecticide chlorpyrifos. Uncertainty in the estimation of each SSD is obtained either in the form of a pointwise percentile confidence interval computed by bootstrap regression or an associated credible interval. We demonstrate that uncertainty in SSD estimation can be reduced by applying a Bayesian approach that incorporates expert knowledge and that use of Bayesian methodology permits estimation of an SSD that is more robust to variations in data. The results suggest that even with sparse data sets theoretical criticisms of the SSD approach can be overcome.

Animals↗

PubMed2004

Kusunda: an Indo-Pacific language in Nepal.

The Kusunda people of central Nepal have long been regarded as a relic tribe of South Asia. They are, or were until recently, seminomadic hunter-gatherers, living in jungles and forests, with a language that shows no similarities to surrounding languages. They are often described as shorter and darker than neighboring tribes. Our research indicates that the Kusunda language is a member of the Indo-Pacific family. This is a surprising finding inasmuch as the Indo-Pacific family is located on New Guinea and surrounding islands. The possibility that Kusunda is a remnant of the migration that led to the initial peopling of New Guinea and Australia warrants additional investigation from both a linguistic and genetic perspective.

Evolution, Molecular↗

PubMed2004

A regulatory framework for controlling effluent discharges using toxicity testing in the UK.

Legislation designed to regulate effluent discharges is expressed in terms of minimising the risk of harm of that discharge to the environment. Practical implementation is usually based on the control and measurement of a limited number of individual chemicals. However, this is not always effective because of the complex nature of some discharges or the lack of data for some chemicals, preventing the definition of acceptable levels in the environment. Direct Toxicity Assessment (DTA) clearly has a role in such circumstances because it avoids the need for a comprehensive chemical characterisation of effluent discharges. Several scenarios in which DTA can play a useful role in water quality management under current legislation have been identified. A 'generic' framework for the implementation of bioassays for effluent control is proposed. This provides a number of options in terms of the level of environmental protection afforded and the 'starting point' for a DTA programme (i.e. whether it is based on local measurable impacts on water quality or directed from the outset towards the risk assessment of particular discharges). A DTA programme can be developed that meets both the technical and regulatory requirements of these different scenarios. Guidance on the design of such programmes for different scenarios is provided.

Animals↗

PubMed2004

Bioassay selection, experimental design and quality control/assurance for use in effluent assessment and control.

In the UK Direct Toxicity Assessment Programme, carried out in 1998-2000, a series of internationally recognised short-term toxicity test methods for algae, invertebrates and fishes, and rapid methods (ECLOX and Microtox) were used extensively. Abbreviated versions of conventional tests (algal growth inhibition tests, Daphnia magna immobilisation test and the oyster embryo-larval development test) were valuable for toxicity screening of effluent discharges and the identification of causes and sources of toxicity. Rapid methods based on chemiluminescence and bioluminescence were not generally useful in this programme, but may have a role where the rapid test has been shown to be an acceptable surrogate for a standardised test method. A range of quality assurance and control measures were identified. Requirements for quality control/assurance are most stringent when deriving data for characterising the toxic hazards of effluents and monitoring compliance against a toxicity reduction target. Lower quality control/assurance requirements can be applied to discharge screening and the identification of causes and sources of toxicity.

Animals↗

PubMed2004

Risk characterisation in direct toxicity assessment of the River Esk and the Tees Estuary.

This paper illustrates the use of deterministic and probabilistic approaches to the ecotoxicological risk assessment of effluents through two simple examples taken from the UK Direct Toxicity Assessment Demonstration Programme. In this study, the direct protection objective for the River Esk in Scotland was the prevention of short-term lethal toxicity to invertebrates from exposure to effluent containing insecticides. Both a deterministic and a probabilistic risk characterisation show that such toxicity is very unlikely to occur. The protection objectives for the Lower Tees Estuary were more complex, due to a variety of discharges and potentially sensitive species. A deterministic risk assessment using the most sensitive species suggests that toxicity will be high at all times. In contrast, a probabilistic risk assessment suggests that, although acute toxicity is considerable, it is not likely to occur at all times or affect all species, and discharge scenarios do exist in which acute toxicity could be relatively low. These two case studies illustrate the use of probabilistic risk assessment in achieving more realistic assessments of effluent toxicity through use of all available data.

Animals↗

PubMed2003

Estimating the effects of 17alpha-ethinylestradiol on populations of the fathead minnow Pimephales promelas: are conventional toxicological endpoints adequate?

Environmental benchmarks have recently been proposed for several steroids including the synthetic steroid, 17alpha-ethinylestradiol (EE2). These benchmarks are based on extrapolation from studies involving long-term exposure of various fish species to EE2. One of the critical studies was a complete life-cycle experiment performed with the fathead minnow Pimephales promelas over a 289 day exposure period. The lowest observed effect concentration (LOEC) and the no observed effect concentration (NOEC) for gonad histology were 4 and 1 ng L(-1) respectively. This was because no testicular tissue could be found in any fish exposed to 4 ng L(-1). In the present paper, the survival and reproduction data from that study are reanalyzed to determine the effects of EE2 on the intrinsic rate of population growth (r = In (lambda)), a parameter of demographic importance. We estimate critical threshold concentrations with respect to r and compare these with those previously derived from conventional toxicity test summaries. Further, we assess the influence of individual variability on threshold estimates using a combination of bootstrap and regression approaches, together with a suite of perturbation analyses. These yield ErC100 values (the concentration estimated to reduce intrinsic growth rate to zero) of 3.11 ng L(-1) (linear model) and 3.41 ng L(-1) (quadratic model), comparable with a maximum acceptable toxicant concentration (MATC) of 2 ng L(-1) for feminization of exposed fish calculated by Laenge et al. Our results indicate that reduction in population growth rate with increasing concentration occurred more through EE2 acting to reduce fertility than survival rates. The significance of these summary statistics when deriving environmental benchmarks for steroid estrogens is discussed in the context of affording protection to populations following long-term exposure.

Animals↗

PubMed2003

Evaluation of probabilistic risk assessment of pesticides in the UK: chlorpyrifos use on top fruit.

The use of probabilistic risk assessment (PRA) for examining chemical impacts has become an important area of debate within the European Union. This paper describes a case study on probabilistic techniques to assess pesticide risks in the UK aquatic environment. The main aim of this paper is to demonstrate both the potential strengths and weaknesses of PRA for assessing pesticides when compared with the conventional deterministic approach, and to examine whether PRA is useful within the European regulatory context. The organophosphate insecticide, chlorpyrifos, was selected as a model compound and toxicity exposure ratios calculated using Monte Carlo analysis and different distributions of spray drift and toxicity values following application to top fruit. Chlorpyrifos is highly toxic to arthropods but less toxic to fishes. Species sensitivity followed a log-normal distribution when fitted to all toxicity data. Toxicity data quantity had little influence on species sensitivity distribution model parameters when n was greater than 10 species. Below this, estimates were less accurate and precise, possibly because of the inclusion of data from many different sources. Estimates of chlorpyrifos exposure derived from the standard spray drift model differed substantially from measurements of chlorpyrifos in European surface waters. When a distribution based on measured concentrations was used in a PRA, the risk of acute fish mortality was low, and the risk of acute arthropod mortality was lower than in other scenarios, although not negligible. If PRA is used to assess pesticides, risk managers need further guidance on how to conduct a PRA and what constitutes 'unacceptable risk' under EC Directive 91/414/EEC, as judgement is required when simple trigger values are no longer used.

Animals↗

PubMed2003

Estimation of demographic toxicity through the double bootstrap.

Toxicity to organisms is usually expressed in terms of an observable effect on individuals from which a summary endpoint (such as the NOEC or ECx) is derived for risk assessment and environmental quality standards. However, toxicity evaluated in terms of a demographic endpoint may be more relevant to such regulatory applications. In this paper the effect of toxicity on population growth rate r is explored in tandem with a 'double bootstrap' to incorporate uncertainty. Exemplifying the approach with a set of individualized life table response data obtained for Daphnia magna exposed to zinc sulphate solution, the influence of increasing concentrations is assessed. A demographic-based metric for r, the ErCx (effect on r concentration percentage), is defined to permit alternative population level estimation of a 'safe effect' concentration.

Animals↗

PubMed2002

Freshwater to saltwater toxicity extrapolation using species sensitivity distributions.

There is generally a lack of saltwater ecotoxicity data for risk assessment purposes, leaving an unknown margin of uncertainty in saltwater assessments that utilize surrogate freshwater data. Consequently, a need for sound scientific advice on the suitability of using freshwater data to extrapolate to saltwater effects exists. Here we use species sensitivity distributions to determine if freshwater datasets are adequately protective of saltwater species assemblages for 21 chemical substances. For ammonia and the metal compounds among these data, freshwater data were generally protective because freshwater organisms tended to be more sensitive. In contrast, for pesticide and narcotic compounds, saltwater species tended to be more sensitive and a suitable uncertainty factor would need to be applied to surrogate freshwater data. Biological and physicochemical factors contribute to such differences in freshwater and saltwater species sensitivities, but the species compositions of datasets used are also important.

Animals↗