Biomedical subjects

Eric P M Grist

Publications and source records attributed to Eric P M Grist.

10 recordsLinked to original sources

PubMed2006

Chronic toxicity of tributyltin to development and reproduction of the European freshwater snail Lymnaea stagnalis (L.).

Chronic toxicity, growth and reproduction were measured in the freshwater gastropod Lymnaea stagnalis exposed to waterborne bis(tri-n-butyltin) oxide (TBTO) over a range of four nominal concentrations (0-10microg TBTl(-1)). Egg development was completely inhibited at 10microg TBTl(-1), whilst abnormal embryonic development was observed at 1microg TBTl(-1). For the solvent control and the 0.01microg TBTl(-1)treatment group, normal development of L. stagnalis was observed. Survivorship of hatchlings was significantly reduced by TBT at 1microgl(-1) while inhibition of shell growth of L. stagnalis was also observed at this concentration. The data were used to determine intrinsic growth rates (r) using two theoretical approaches (the Euler-Lotka equation and a Leslie Matrix). Both approaches showed that survival, fecundity and population growth rate were reduced at 1microg TBTl(-1). Interestingly, at 0.01microg TBTl(-1) snails showed a higher fecundity and growth rate than in the solvent control. The TBT concentration at which the r would equal zero (ECr(0)) and the population NOEC (No Observed Effect Concentration) were estimated. The population NOEC was defined as either the lower 95% confidence or lower 95% pointwise percentile limit of the ECr(0). Values obtained using the two different approaches were similar and thus a geometric mean was calculated to obtain a final representative population NOEC value for L. stagnalis of 2745ng TBTl(-1). The present data together with chronic toxicity TBT data for freshwater organisms, obtained from peer-reviewed literature, were used to construct a species sensitivity distribution (SSD). A predicted no effect concentration was then derived from the SSD (hazardous concentration at 5%, i.e., HC5 or 95% protection level). This SSD was compared with the SSD derived from saltwater species datasets. The HC5 value for saltwater species (3.55ng TBTl(-1); lower confidence limit: 1.93ng TBTl(-1)) was significantly lower than that for freshwater species (30.13ng TBTl(-1); lower confidence limit: 9.23ng TBTl(-1)), indicating that saltwater species are probably more susceptible to TBT than their freshwater counterparts.

Animals↗

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↗

PubMed2005

Transmissible spongiform encephalopathy risk assessment: the UK experience.

Transmissible spongiform encephalopathy (TSE) risk assessments undertaken in the United Kingdom have mainly had the objective of determining the risks posed to humans from exposure to the causal agents associated with bovine spongiform encephalopathy (BSE) and variant Creutzfeld-Jakob disease (vCJD). In this article, I examine 19 of these risk assessments published to date and consider how their results might be influenced by underlying model assumptions and methodology. Three separate aspects common to all the assessments are infective load estimation, exposure pathway identification, and risk estimation. These are each discussed in detail.

Animals↗

PubMed2005

An evaluation of United Kingdom environmental bovine spongiform encephalopathy risk assessment.

As a member of the group of diseases known as transmissible spongiform encephalopathies (TSEs), bovine spongiform encephalopathy (BSE) has been causally associated with a new variant of Creutzfeldt-Jakob disease (vCJD) in humans. Given the many uncertainties on the transmission and persistence of TSE pathogens in the environment, quantitative assessment of risks to humans and animals continues to remain a public health issue. This paper reviews quantitative BSE risk assessments undertaken in the United Kingdom since 1997 to address the potential for human exposure and theoretical health risks through environmental pathways. The review focuses on how model assumptions and methodology may influence the results.

Animals↗

PubMed2003

Uptake and depuration of 4-nonylphenol by the benthic invertebrate Gammarus pulex: how important is feeding rate?

The major exposure and uptake route for soluble toxins by aquatic organisms is generally considered to be through the water column. In the case of hydrophobic chemicals, exposure and uptake through diet often take on greater importance as the chemicals adsorb onto organic sediments and food. A chemical that has recently come under close scrutiny because of its toxicity and possible endocrine disrupting effects in aquatic life is 4-nonylphenol (NP). It has been detected in environmental water and sediment samples and is a persistent and hydrophobic (log KOW = 4.48) contaminant in many aquatic systems. In this study, the relative importance of NP uptake through accumulation from diet and water was examined for the detritus-feeding freshwater shrimp Gammarus pulex. Using a bootstrap nonlinear regression technique, the level of toxin present in G. pulex at any time during or after initial exposure was estimated. Heterogeneity, together with assumptions on feeding rate, was shown to affect the determination of NP uptake substantially. Because of its lifestyle as a benthic organism, the main exposure route was at first assumed to be through sediments and food. However, the results suggest that major uptake may also occur through water. The statistical and modeling methodology may be applied to uptake and depuration assessments for any aquatic organisms exhibiting a variable feeding phase.

Amphipoda↗

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

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

Time should be considered in developmental ecotoxicity test.

Developmental toxicity tests are often used for the hazard assessment of chemicals and environmental media. One of the most widely used is the oyster embryo larval test (OEL), in which the development of oyster larvae is arrested at a single fixed time (e.g. 24 or 48 h) of toxic exposure, and the proportion of normal larvae measured. However, a major problem with this conventional approach is the lack of information on temporal trends in development. In this study, Pacific oyster Crassostrea gigas embryos were exposed to nominal concentrations of copper (CUSO4) of <0.001 (control), 0.60,1.25,2.5, 5.0, 10.0 and 20.0 microg l(-1) (at 20 degrees C, salinity 35 per thousand and pH 8.1). Three replicates from each group were arrested and examined every 8 h during 24-72 h of exposure, and the number of viable larvae developed to D-shape was determined. The results revealed that the number of viable D-shape larvae in the control increased rapidly and reached an optimum at 32 h, before declining gradually due to starvation. Analysis of covariance (ANCOVA) showed that larval developmental rates during 0-32 h were significantly inhibited by Cu at all concentrations. This paper demonstrates that arrest and measurement at different time periods are important and should be incorporated into the OEL test. This would maximise the sensitivity of the test in detecting developmental effects in spiked or environmental samples.

Animals↗

PubMed2002

Better bootstrap estimation of hazardous concentration thresholds for aquatic assemblages.

The introduction of species sensitivity distribution (SSD) approaches to ecological risk assessment offers the potential for a more transparent scientific basis for the derivation of predicted no-effect concentrations. However, conventional SSD methodologies have relied on standard distributions (e.g., log logistic, log normal) that are not necessarily based on sound ecological or statistical grounds. More recently, bootstrap resampling techniques that do not rely on distributional assumptions have been applied to the problem. Here we describe how a more advanced bootstrap methodology may be applied to derive better point estimates and confidence intervals for SSD estimates of safe environmental concentrations. Motivated by the fact that the true SSD may not fit any standard model category, we go on to consider a hybrid bootstrap regression approach. This can yield a substantially different estimate for the SSD when compared with both the basic bootstrap and the more frequently used parametric curve approaches. With increasing use of SSDs in ecological risk assessment, it is now imperative that the scientific community develops agreement over appropriate methods for their derivation.

Data Interpretation, Statistical↗

PubMedDate not supplied

Chronic toxicity of tributyltin on development and reproduction of the hermaphroditic snail Physa fontinalis: Influence of population density.

Tributyltin (TBT) is toxic to aquatic organisms and occurs widely in sediments and surface waters of American and European rivers and lakes. This study investigated TBT effects on development and population growth rate (r) of the common, hermaphroditic European freshwater snail Physa fontinalis. Egg ropes of similar age (1-3 days old) were exposed to a control (solvent only) and nominal concentrations of 0.01, 1.0 and 10 microg TBT l(-1) in triplicate. Hatching and mortality were recorded during 0-40 days of exposure. At day 40, 18 juveniles were randomly selected from each concentration (i.e., six from each test vessel) and individually exposed to the same concentration of TBT in 50 ml beakers. A cohort of 20 juveniles was allowed to continue developing in the original test vessels, so that individual and grouped results could be compared. Mortality and reproduction were recorded at 48-h intervals throughout the study period (110 days). Abnormal embryonic development was observed at 1 and 10 microg TBT l(-1). Although 50% of eggs hatched at 10 microg TBT l(-1), all these hatchlings failed to survive. Survivorship of hatchlings was significantly reduced by TBT at 1 microgl(-1). In general, there was a delay in egg production in isolated snails when compared with the grouped snails. Survival, fecundity and population growth rate (r) were reduced in both individual and grouped P. fontinalis at 1.0 microg TBT l(-1). Only a decline in r was observed in snails exposed individually to 0.01 microg TBT l(-1).

Animals↗