Distributions of concentrations of bisphenol A in North American and European surface waters and sediments determined from 19 years of monitoring data.

Concentrations of bisphenol A (BPA) in North American and European fresh and marine surface waters and sediments were analyzed to quantify environmental levels and evaluate trends over the years 1996-2014. In North American surface water and sediment, 68% of 1030 weighted observations were below a detection limit (varied widely between studies). In Europe, 33% of 5057 weighted observations were below a detection limit. In North America and Europe, 50th percentile concentrations were 0.005 µg L-1 and 0.029 µg L-1 in freshwater and 0.0011 µg L-1 and 0.007 µg L-1 in marine water. The 95th percentile concentrations in freshwater were the same in North America and Europe at 0.30 µg L-1 and were 0.024 µg L-1 and 0.15 µg L-1 in marine water, respectively. Fiftieth percentile concentrations in North American and European freshwater sediment were 0.7 ng g-1 dry weight (dw) and 7.0 ng g-1 dw and in marine sediment were 1.0 ng g-1 dw and <0.03 ng g-1 dw, respectively. The 95th percentile concentrations were 39 ng g-1 dw and 177 ng g-1 dw in freshwater sediment and 100 ng g-1 dw and 63 ng g-1 dw in marine sediment, respectively. Most concentrations were below published chronic toxicity values or regulatory limits. BPA freshwater concentrations in both regions appear to have remain relatively unchanged over the 19 year period during which BPA production and use in polycarbonate plastic production increased significantly. There is no clear correlation between BPA or polycarbonate production and BPA levels in surface waters.

Adult fathead minnow, Pimephales promelas, partial life-cycle reproductive and gonadal histopathology study with bisphenol A.

Bisphenol A (BPA) is an intermediate used to produce epoxy resins and polycarbonate plastics. Although BPA degrades rapidly in the environment with aquatic half-lives from 0.5 to 6 d, it can be found in aquatic systems because of widespread use. To evaluate potential effects from chronic exposure, fathead minnows were exposed for 164 d to nominal concentrations of 1, 16, 64, 160, and 640 µg/L BPA. Population-level endpoints of survival, growth, and reproduction were assessed with supplemental endpoints (e.g., vitellogenin, gonad histology), including gonad cell type assessment and quantification. No statistically significant changes in growth, gonad weight, gonadosomatic index, or reproduction variables (e.g., number of eggs and spawns, hatchability) were observed; however, there was a significant impact on male survival at 640 µg/L. Vitellogenin increased in both sexes at 64 µg/L or higher. Gonad cell type frequencies were significantly different from controls at 160 µg/L or higher in males with a slight decrease in spermatocytes compared with less mature cell types, and at 640 µg/L in females with a slight decrease in early vitellogenic cells compared with less mature cells. The decrease in spermatocytes did not correspond to a decrease in the most mature sex cell type (spermatozoa) and did not impair male fertility, as hatchability was not impacted. Overall, marginal shifts in gametogenic cell maturation were not associated with any statistically significant effects on population-relevant reproductive endpoints (growth, fecundity, and hatchability) at any concentration tested.

Multi-criteria decision analysis of test endpoints for detecting the effects of endocrine active substances in fish full life cycle tests.

Fish full life cycle (FFLC) tests are increasingly required in the ecotoxicological assessment of endocrine active substances. However, FFLC tests have not been internationally standardized or validated, and it is currently unclear how such tests should best be designed to provide statistically sound and ecologically relevant results. This study describes how the technique of multi-criteria decision analysis (MCDA) was used to elicit the views of fish ecologists, aquatic ecotoxicologists and statisticians on optimal experimental designs for assessing the effects of endocrine active chemicals on fish. In MCDA qualitative criteria (that can be valued, but not quantified) and quantitative criteria can be used in a structured decision-making process. The aim of the present application of MCDA is to present a logical means of collating both data and expert opinions on the best way to focus FFLC tests on endocrine active substances. The analyses are presented to demonstrate how MCDA can be used in this context. Each of 3 workgroups focused on 1 of 3 species: fathead minnow (Pimephales promelas), Japanese medaka (Oryzias latipes), and zebrafish (Danio rerio). Test endpoints (e.g., fecundity, growth, gonadal histopathology) were scored for each species for various desirable features such as statistical power and ecological relevance, with the importance of these features determined by assigning weights to them, using a swing weighting procedure. The endpoint F1 fertilization success consistently emerged as a preferred option for all species. In addition, some endpoints scored highly in particular species, such as development of secondary sexual characteristics (fathead minnow) and sex ratio (zebrafish). Other endpoints such as hatching success ranked relatively highly and should be considered as useful endpoints to measure in tests with any of the fish species. MCDA also indicated relatively less preferred endpoints in fish life cycle tests. For example, intensive histopathology consistently ranked low, as did measurement of diagnostic biomarkers, such as vitellogenin, most likely due to the high costs of these methods or their limited ecological relevance. Life cycle tests typically do not focus on identifying toxic modes and/or mechanisms of action, but rather, single chemical concentration-response relationships for endpoints (e.g., survival, growth, reproduction) that can be translated into evaluation of risk. It is, therefore, likely to be an inefficient use of limited resources to measure these mechanism-specific endpoints in life cycle tests, unless the value of such endpoints for answering particular questions justifies their integration in specific case studies.

Is it safe to pool the blank control data with the solvent control data?

Ecotoxicological studies, where the test chemical is dosed with a solvent, are often performed using two controls, a blank control (BC) and a solvent control (SC). In many guidelines, it is recommended to combine the data from the BC and the SC if they do not differ significantly and otherwise only use the data from the SC for the significance test on the effects of the chemical treatment. In this paper the validity of the conditional testing scheme is investigated by simulating data sets with and without difference between BC and SC. These simulations show that this testing scheme does not lead to a valid statistical test.

Exposure analysis of bisphenol A in surface water systems in North America and Europe.

This study was conducted to develop a statistical understanding of exposures to bisphenol A (BPA) in aquatic environments in North America and Europe. Concentrations of BPA have been reported by 89 investigations published between 1997 and 2007. On the basis of an analysis of weighted observations (n = 1068 and 848 for North America and Europe, respectively), BPA was reported at concentrations above the detection limit in 20-51% of freshwater samples. Median BPA concentrations for fresh surface waters for North America and Europe were 0.081 and 0.01 microg/L, respectively, while 95th percentiles were 0.47 and 0.35 microg/L, respectively. In contrast to fresh surface waters, only limited data are available for sediments and less for marine ecosystems. For freshwater sediments in North America (n = 71), the median and 90th percentile concentration (the 95th percentile was not calculable) were 0.6 and 3.4 ng/ g-dw, respectively, while the median and 95th percentile concentration in Europe (n = 249) were 16 and 256 ng/g-dw, respectively. To assess the potential ecological significance, we compared exposure concentrations with available regulatory criteria. The results suggest the frequency of locations in which concentrations are likely to cause adverse effects on aquatic ecosystems is low, with the exception of sediments collected from some highly urbanized and industrial locations.

Effects of bisphenol a on fecundity, egg hatchability, and juvenile growth of Marisa cornuarietis.

Recent work on the snail Marisa cornuarietis has claimed to show endocrine disruption in response to bisphenol A (BPA). The present experimental design was optimized to detect effects of BPA on fecundity, egg hatchability, and juvenile growth, with an emphasis on reproduction, since previous studies suggested this to be a sensitive endpoint. No differences in eggs/female/ month between unexposed snails and snails exposed to nominal concentrations of 0.1, 1, 25, and 640 microg BPA/L during six months of exposure were found. No effect of BPA on the percentage of eggs hatching successfully was found, as was no difference in time to hatching between the control and any BPA treatment. We observed a significant decrease in female growth and a marginal effect on female wet weight in the 640-microg/L treatment compared to the control and a significant increase in male growth rate and a marginal increase in male wet weight in the 1-microg/L treatment compared to the control. However, a much greater proportion of the variability in juvenile growth was explained by variation between pairs and between siblings from the same pair than by BPA treatment. We conclude that effects of BPA in the nominal exposure range 0.1 to 640 microg/L (measured range 0.062-696 microg/L) are unlikely to be of significance for field populations of this species. An additional adult fecundity trial at 22 degrees C (in contrast to all other experiments that were conducted at 25 degrees C) found no evidence to suggest that snails are more sensitive to BPA at the lower temperature, as has been previously claimed. The present results indicate that the sensitivity of M. cornuarietis to BPA is similar to that of other aquatic invertebrates for which data are available.

Calculation of the minimum significant difference at the NOEC using a non-parametric test.

The minimum significant difference (MSD) at the no observed effect concentration (NOEC) is required in many guidelines for standardised ecotoxicological tests. A method is given to calculate the MSD if non-parametric pair-wise comparison of each concentration with the control is used to determine the NOEC.

Does bisphenol A induce superfeminization in Marisa cornuarietis? Part I: intra- and inter-laboratory variability in test endpoints.

It has been claimed that bisphenol A (BPA) induces superfeminization in the freshwater gastropod, Marisa cornuarietis. To explore the reproducibility of prior work, here we present results from a three-laboratory study, the objectives of which were to determine the mean and variability in test endpoints (i.e., adult fecundity, egg hatchability, and juvenile growth) under baseline conditions and to identify the sources of variability. A major source of variability for all of the measured endpoints was due to differences within and among individuals. With few exceptions, variability among laboratories and among replicate tanks within laboratories contributed little to the observed variability in endpoints. The results highlight the importance of obtaining basic knowledge of husbandry requirements and baseline information on life-history traits of potential test species prior to designing toxicity test protocols. Understanding of the levels and sources of endpoint variability is essential so that statistically robust and ecologically relevant tests of chemicals can be conducted.

Does bisphenol A induce superfeminization in Marisa cornuarietis? Part II: toxicity test results and requirements for statistical power analyses.

This study presents results of the effects of bisphenol A (BPA) on adult egg production, egg hatchability, egg development rates and juvenile growth rates in the freshwater gastropod, Marisa cornuarietis. We observed no adult mortality, substantial inter-snail variability in reproductive output, and no effects of BPA on reproduction during 12 weeks of exposure to 0, 0.1, 1.0, 16, 160 or 640 microg/L BPA. We observed no effects of BPA on egg hatchability or timing of egg hatching. Juveniles showed good growth in the control and all treatments, and there were no significant effects of BPA on this endpoint. Our results do not support previous claims of enhanced reproduction in Marisa cornuarietis in response to exposure to BPA. Statistical power analysis indicated high levels of inter-snail variability in the measured endpoints and highlighted the need for sufficient replication when testing treatment effects on reproduction in M. cornuarietis with adequate power.

Current issues in statistics and models for ecotoxicological risk assessment.

A review is given on statistical and modelling issues in ecotoxicology. The issues discussed are: 1. How to estimate an (almost) no effect concentration chemicals in the laboratory. 2. Combining single-species acceptable effect levels to an acceptable effect level for a multi-species ecosystem. 3. The combined effect of exposure to several chemicals. 4. Bioavailability in the natural environment and food-web models. Most current procedures in setting standards allow the environmental concentration to be above the acceptable effect concentration for a small fraction of the species. It is shown that a considerable part of the fraction of the affected species will suffer a severe effect.

Egg distributions and the information a solitary parasitoid has and uses for its oviposition decisions.

Approximately three decades ago the question was first answered "whether parasitoids are able to assess the number or origin of eggs in a host" for a solitary parasitoid, Leptopilina heterotoma, by fitting theoretically derived distributions to empirical ones. We extend the set of different theoretically postulated distributions of eggs among hosts by combining searching modes and abilities in assessing host quality. In the models, parasitoids search either randomly (Poisson) (1) or by vibrotaxis (Negative Binomial) (2). Parasitoids are: (a) assumed to treat all hosts equally, (b) able to distinguish them in unparasitised and parasitised hosts only, (c) able to distinguish them by the number of eggs they contained, or (d) able to recognise their own eggs. Mathematically tractable combinations of searching mode (1 and 2) and abilities (a,b,c,d) result in seven different models (M1a, M1b, M1c, M1d, M2a, M2b and M2c). These models have been simulated for a varying number of searching parasitoids and various mean numbers of eggs per host. Each resulting distribution is fitted to all theoretical models. The model with the minimum Akaike's information criterion (AIC) is chosen as the best fitting for each simulated distribution. We thus investigate the power of the AIC and for each distribution with a specified mean number of eggs per host we derive a frequency distribution for classification. Firstly, we discuss the simulations of models including random search (M1a, M1b, M1c and M1d). For M1a, M1c and M1d the simulated distributions are correctly classified in at least 70% of all cases. However, in a few cases model M1b is only properly classified for intermediate mean values of eggs per host. The models including vibrotaxis as searching behaviour (M2a, M2b and M2c) cannot be distinguished from those with random search if the mean number of eggs per host is low. Among the models incorporating vibrotaxis the three abilities are detected analogously as in models with random search. Experiments with two species of solitary parasitoids (L. heterotoma and Asobara tabida) are conducted. All theoretically postulated distributions are separately fitted to the resulting experimental egg distributions. The AIC criterion is used to choose the best fitting theoretical distribution. For both parasitoid species the frequency distribution of best fitting models for experimental data is compared to the classification of distributions generated by simulations. This leads to the conclusion that both L. heterotoma and A. tabida are able to distinguish between parasitised and unparasitised hosts. For L. heterotoma the results point to an ability to assess the number of eggs in a host, whereas A. tabida does not seem to have this ability. This difference suggests that an egg is more valuable for L. heterotoma than for A. tabida.