Population-level impacts of pesticide-induced chronic effects on individuals depend more on ecology than toxicology.

The current method for assessing long-term risk of pesticides to mammals in the EU is based on the individual rather than the population-level and lacks ecological realism. Hence there is little possibility for regulatory authorities to increase ecological realism and understanding of risks at the population-level. Here we demonstrate how, using ABM modelling, assessments at the population-level can be obtained even for a pesticide with complex long-term effects such as epigenetic transmission of reproductive depression. By objectively fitting nonlinear models to the simulation outputs it was possible to compare population depression and recovery rates for a range of scenarios in which toxicity and exposure factors were varied. The system was differentially sensitive to the various factors, but vole ecology and behaviour were at least as important predictors of population-level effects as toxicology. This emphasises the need for greater focus on animal ecology in risk assessments.

Conceptual model for improving the link between exposure and effects in the aquatic risk assessment of pesticides.

Assessment of risks to aquatic organisms is important in the registration procedures for pesticides in industrialised countries. This risk assessment consists of two parts: (i) assessment of effects to these organisms derived from ecotoxicological experiments (=effect assessment), and (ii) assessment of concentration levels in relevant environmental compartments resulting from pesticide application (=exposure assessment). Current procedures lack a clear conceptual basis for the interface between the effect and exposure assessments which may lead to a low overall scientific quality of the risk assessment. This interface is defined here as the type of concentration that gives the best correlation to ecotoxicological effects and is called the ecotoxicologically relevant concentration (ERC). Definition of this ERC allows the design of tiered effect and exposure assessments that can interact flexibly and efficiently. There are two distinctly different exposure estimates required for pesticide risk assessment: that related to exposure in ecotoxicological experiments and that related to exposure in the field. The same type of ERC should be used consistently for both types of exposure estimates. Decisions are made by comparing a regulatory acceptable concentration (=RAC) level or curve (i.e., endpoint of the effect assessment) with predicted environmental concentration (=PEC) levels or curves (endpoint of the exposure assessment). For decision making based on ecotoxicological experiments with time-variable concentrations a tiered approach is proposed that compares (i) in a first step single RAC and PEC levels based on conservative assumptions, (ii) in a second step graphically RAC and PEC curves (describing the time courses of the RAC and PEC), and (iii) in a third step time-weighted average RAC and PEC levels.

Effects on the function of three trophic levels in marine plankton communities under stress from the antifouling compound zinc pyrithione.

This study aimed to investigate functional responses of natural marine planktonic communities to stress from the antifouling compound zinc pyrithione (ZPT). Isotope labelling techniques (14C) were applied to study bacterial incorporation of leucine, photosynthetic activity of phytoplankton and grazing of labelled prey by zooplankton communities for 6 days after exposures to nominal concentrations of 0, 5, 25, 50 nM ZPT in a mesocosm experiment in Isefjord, Denmark. Significant direct effects were visible on chlorophyll a concentrations, which decreased in all exposed communities, to between 48 and 36% of control concentrations on Day 3, 1 day after the last exposure. Phytoplankton activities were also significantly affected on Day 3 with activities between 9 and 26% of control levels, as was zooplankton activities in the 25 and 50 nM exposures. In the 50 nM exposure the total community zooplankton activity was reduced to 25+/-4%, and per individual to 46+/-11% of control levels. Bacterial communities showed positive indirect effects with high activities (up to 183+/-40%) due to higher amounts of available substrate from algal death. Pollution induced community tolerance analyses performed on phytoplankton and bacterial communities at the end of the experiment indicated a development of increased tolerance for phytoplankton in the 50 nM exposed communities, whereas there were no changes in tolerance in the bacterial communities. Multivariate analysis of the integrated functional response by the plankton communities revealed a significant difference (p<0.05) between exposed communities compared to controls in the first 3 days after last exposure and in the end of the experiment. The study provides evidence of diverse effects on the functions of marine plankton communities under stress from a pollutant. Direct effects lead to cascading indirect effects throughout the community, eventually causing different developments. Continuous exposure to ZPT could lead to severe long-term effects, causing more permanent changes in structure and function than observed here. The study demonstrates that it is possible to assess the functional effects of a stressor in a complex mesocosm system, and to determine effects in a complex plankton community, which were not predictable from laboratory studies.

Assessing pesticide risks to threatened and endangered species using population models: Findings and recommendations from a CropLife America Science Forum.

This brief communication reports on the main findings and recommendations from the 2014 Science Forum organized by CropLife America. The aim of the Forum was to gain a better understanding of the current status of population models and how they could be used in ecological risk assessments for threatened and endangered species potentially exposed to pesticides in the United States. The Forum panelists' recommendations are intended to assist the relevant government agencies with implementation of population modeling in future endangered species risk assessments for pesticides. The Forum included keynote presentations that provided an overview of current practices, highlighted the findings of a recent National Academy of Sciences report and its implications, reviewed the main categories of existing population models and the types of risk expressions that can be produced as model outputs, and provided examples of how population models are currently being used in different legislative contexts. The panel concluded that models developed for listed species assessments should provide quantitative risk estimates, incorporate realistic variability in environmental and demographic factors, integrate complex patterns of exposure and effects, and use baseline conditions that include present factors that have caused the species to be listed (e.g., habitat loss, invasive species) or have resulted in positive management action. Furthermore, the panel advocates for the formation of a multipartite advisory committee to provide best available knowledge and guidance related to model implementation and use, to address such needs as more systematic collection, digitization, and dissemination of data for listed species; consideration of the newest developments in good modeling practice; comprehensive review of existing population models and their applicability for listed species assessments; and development of case studies using a few well-tested models for particular species to demonstrate proof of concept. To advance our common goals, the panel recommends the following as important areas for further research and development: quantitative analysis of the causes of species listings to guide model development; systematic assessment of the relative role of toxicity versus other factors in driving pesticide risk; additional study of how interactions between density dependence and pesticides influence risk; and development of pragmatic approaches to assessing indirect effects of pesticides on listed species.

Genetic population structure of the prosobranch snail Potamopyrgus antipodarum (Gray) in Denmark using PCR-RAPD fingerprints.

Parthenogenetic species are often more widely distributed geographically than their sexual relatives. This success in colonizing can be explained either by dispersal of one or a few clones of wide physiological tolerance or by the distribution of many locally adapted clones. Here we test the hypothesis that successfully invading clones of Potamopyrgus antipodarum (Gray) are composed of a few broadly adapted genotypes by using polymerase chain reaction random amplified polymorphic DNA (PCR-RAPD) fingerprinting on six different populations of P. antipodarum from Denmark and three morphotypes of P. antipodarum from Britain. We detected two genotypes of P. antipodarum in six populations examined across Denmark using four decamer primers. The two genotypes were found to be morphologically and genetically indistinguishable from British P. antipodarum. In five of the six Danish populations only one genotype was found; at the remaining site, the two genotypes occurred sympatrically. The present study suggests that P. antipodarum successfully invaded Europe by the proliferation of very few clones.

Evaluation of cadmium, copper, zinc, and iron concentrations and tissue distributions in the benthic crab, Dorippe granulata (De Haan, 1841) from Tolo Harbour, Hong Kong.

The distributions of copper, zinc, iron, and cadmium among the tissues of Dorippe granulata were determined. The highest copper concentrations were found in the haemolymph (c. 53 microg ml(-1)) while the highest iron concentrations occurred in the gills (c. 720 microg g(-1) dry weight) and the highest zinc concentrations in the exoskeleton (c. 200 microg g(-1) dry weight). By comparison, concentrations of the non-essential metal, cadmium, were low in all tissues (mean = 10 microg g(-1) dry weight). The highest value was recorded from the midgut gland of a female crab (18.5 microg Cd g(-1) dry weight). Concentrations of copper, zinc, and iron were positively correlated with tissue-hydration levels. Such a relationship was not found for cadmium. The findings are discussed with regard to trace-metal levels found in temperate and tropical brachyurans from clean and polluted localities.

Metabolism of the polycyclic aromatic hydrocarbon fluoranthene by the polychaete Capitella capitata species I.

Previous studies have shown that infaunal deposit feeders may enhance the loss of organic contaminants from sediments. However, the extent to which this occurs as a result of sediment microbial stimulation, porewater flushing, or biotransformation by infauna remains unclear. The purpose of this study was to determine whether the infaunal polychaete Capitella sp. I is able to metabolize the polycyclic aromatic hydrocarbon (PAH) fluoranthene and to provide an initial characterization of the metabolites produced. Our results showed that Capitella sp. I is able to metabolize fluoranthene to more hydrophilic products and that, after 24 h in clean sediment, fluoranthene could no longer be detected in worm tissues whereas a number of fluoranthene-derived metabolites were present. None of the metabolites released or retained by worms resembled known bacterial metabolites, suggesting that Capitella, and not bacteria associated with its gut or body surface, were responsible for the biotransformation of fluoranthene in our system. On the basis of ultraviolet maxima, peak shape, relative height, and order of elution, tentative identities of two metabolites (i.e., 3- and 8-hydroxyfluoranthene) are proposed. The results demonstrate that, in addition to their effects on sediment geochemical properties, infaunal polychaetes such as Capitella can enhance the degradation of sediment-associated contaminants by directly metabolizing them.

Are current species extrapolation models a good basis for ecological risk assessment?

Extrapolating the effects of toxicants with either the fixed application factor approach or one of the species sensitivity distribution models currently in widespread use presumes that toxicant effects on single, individual-level endpoints (e.g., survival, fecundity, and growth) reflect effects at the population level. Here, we consider if extrapolations derived on the basis of individual-level endpoints might be misleading with regard to risk assessment and, hence, risk management decisions for ecosystems. Both analytically and by simulation, we demonstrate that for populations with multiplication rates close to one, effects of toxicants at the population level likely are less than or equal to effects on individual life-cycle traits, suggesting that risk assessments based on the latter likely are protective of population-level impacts. We used Monte Carlo simulations to explore how both the frequency of different life-cycle types in a community as well as their relative sensitivity to toxicants influence the toxicant sensitivity distribution of the community as a whole. We compared the output of our simulations with predicted no-effect concentrations derived by an application factor approach and a log-normal distribution-based model, using no-observed-effect concentrations for juvenile survival as input variables in both cases. Our analyses suggest that current extrapolation approaches appear to be protective, and may often be very overprotective, but we have identified conditions in which this may not be the case. We recommend that additional consideration be given to the relative frequency of different life-cycle types, to the proportions of sensitive and insensitive taxonomic groups in communities, and to the role of density-dependent influences on population dynamics to ensure that we develop environmental quality criteria that are sufficiently--but not overly--protective.

Variation in cadmium uptake, feeding rate, and life-history effects in the gastropod potamopyrgus antipodarum: linking toxicant effects on individuals to the population level.

A life-table response experiment was performed to investigate the effects of sediment-bound cadmium on individual life-history traits and feeding rates of four clones of Potamopyrgus antipodarum. Demographic effects were evaluated using a simple two-stage model to estimate population growth rate (lambda). Decomposition analysis was performed to investigate the contributions of each of the affected life-history traits to the effects observed on lambda, and elasticity analysis was applied to examine the relative sensitivity of lambda to changes in each of the life-history traits. Interclonal differences in tolerance to sediment-bound cadmium were statistically significant but were within an order of magnitude. There were no consistent patterns among clones in terms of which individual life-history trait was most or least sensitive to cadmium exposure. The relative performance of clones did not rank consistently across the cadmium gradient and was dependent on which trait was measured. Although lambda was most sensitive to changes in survival terms, the effects of cadmium on time to first reproduction and reproductive output were the major causes of reductions in lambda. Large percent reductions in some of the individual life-history traits were attenuated at the population level, but very small effects on population growth rate were statistically significant.

Nonylphenol stimulates fecundity but not population growth rate (lambda) of Folsomia candida.

The toxicity of nonylphenol (NP) to springtails was pronounced at 40 mg/kg dry weight soil, at which no animals survived. Body length and fecundity were the individual life-history traits significantly stimulated by sublethal concentrations of NP during a 64-day experiment. However, the effects of NP on these traits did not result in a statistically significant increase in population growth rate (lambda). Decomposition analysis indicated that fecundity was the main contributor to the (non-significant) changes observed in lambda. However, since the elasticity of fecundity was very low, large changes in fecundity resulted in a minimal effect on lambda. Juvenile survival had the highest elasticity of all traits, but was not affected by NP, and therefore did not contribute to effects on lambda. This study confirms previous studies showing that effects of chemicals on individual life-history traits are attenuated at the population level and that lambda is an appropriate endpoint for ecotoxicological studies.

Sources and implications of variability in sensitivity to chemicals for ecotoxicological risk assessment.

Variability among individuals in their responses to toxic chemicals arises from several sources, the most important of which are genetic differences, environmental influences (including maternal effects and historical factors) and measurement error. Effective risk assessment requires that estimates of toxicant response (e.g., LD50, EC50, LOEC, NOEC) are precise--that is, have narrow confidence limits-, repeatable--that is, different laboratories must obtain the same or very similar result-, and accurate--that is, they must provide a reasonable approximation of the effects of toxicants on real ecological systems. Determining which of the above-mentioned sources of variability has the greatest influence on toxicant response has implications for both the design and interpretation of ecotoxicological tests. If, for example, genetic influences are of overriding importance, controlling genotype (by using clones or inbred strains) can lead to greater precision but at the expense of accuracy when the objective is to estimate toxicant response for the species as a whole. Likewise, if environmental influences are of primary importance in controlling the response to toxicants, performing experiments under a standard temperature, light, and food regime may provide highly repeatable test results that have little relevance to the responses of populations in nature. Although there is little doubt that the development of standard ecotoxicological test guidelines (e.g., by the OECD), that control genetic and environmental sources of variability, has led to improvements in the practice of risk assessment, further advances will require a more sophisticated approach for dealing with these sources of uncertainty. There is a need for more systematic approaches for quantifying the sources of variability in toxicant response and for formally combining the error associated with each source in key risk assessment endpoints.

Interclonal variation in the acute and delayed toxicity of cadmium to the European prosobranch gastropod Potamopyrgus antipodarum (Gray).

The lethal responses of three European clones--A, B, and C-of the prosobranch snail Potamopyrgus antipodarum to acute cadmium exposure were examined by the use of a conventional LC50 test and a delayed toxicity test. The questions addressed were: (1) Are there differences in susceptibility (LC50 values and uniformity of response) among the three European clones of P. antipodarum? (2) Are the patterns of differences in susceptibility among clones observed in the LC50 test also observed for the delayed toxicity test? (3) Is there concordance in the ranking of susceptibility among clones under acute cadmium exposure and under chronic cadmium exposure? The results showed that the widths of the tolerance distribution differed among clones. Clones A and B had a steeper slope than clone C (for clone A the difference was marginally significant), which indicates that individuals from clones A and B showed a more uniform response to acute lethal cadmium stress than individuals from clone C. On the basis of the measured differences in LC50 values, clone A individuals showed the highest tolerance to acute cadmium (LC50 value: 1.92 mg Cd L(-1)) followed by clone B (LC50 value: 1.29 mg Cd L(-1)) and clone C (LC50 value: 0.56 mg Cd L(-1)). Clone C was significantly less tolerant than clones A and B. The delayed toxicity test showed a similar pattern to the LC50 test with regard to tolerance differences among clones; however, mortality continued following transfer to clean water, indicating that cadmium was lethal at much lower concentrations than indicated by the conventional LC50 test. Results of the LC50 test and the delayed toxicity test in the present study were in general agreement with results from chronic cadmium exposure experiments (Jensen et al. [2000] Ecol Appl [submitted]), i.e., the least susceptible clone A in the acute cadmium exposure test was also the least susceptible clone in the chronic cadmium exposure test. Based on the dramatic differences between the LC50 and the cadmium exposure concentrations causing delayed toxicity, we suggest that the potential for delayed toxicity should be given greater consideration in ecotoxicity testing.

The influence of nonylphenol on life-history of the earthworm Dendrobaena octaedra Savigny: linking effects from the individual- to the population-level.

We conducted a study to look at the effects of nonylphenol (NP) on the life-history of the parthenogenetic earthworm, Dendrobaena octaedra. During a 196-day study, we observed that the growth rate of juveniles and the percentage of worms producing cocoons were the only traits significantly affected by NP, while the total number of cocoons produced was marginally affected. Despite some fairly large changes in the average values of individual life-history traits caused by NP, the effects were difficult to detect statistically due to large interindividual variability. A declining trend was observed for population growth rate (lambda) with increasing NP concentration, but the decline was not statistically significant. The percent reduction in lambda was less than the percent reduction in the most sensitive life-history trait (fecundity). An elasticity analysis showed that lambda was more sensitive to changes in survival than to changes in reproductive traits. However, neither juvenile nor adult survival were affected by NP, and decomposition analysis showed that the minor changes in lambda were mainly caused by effects of NP on time to first reproduction, time between reproduction events and fecundity. The present study suggests that extrapolation from laboratory studies to population effects in the field may be greatly enhanced by combining ecotoxicological and demographic methods.

Population responses to acute and chronic cadmium exposure in sexual and asexual estuarine gastropods.

: The acute lethal and chronic sublethal responses of sexual (Hydrobia ventrosa) and asexual (Potamopyrgus antipodarum) gastropod populations to cadmium exposure were examined. Three questions were addressed: (i) are there differences in responses of sexual and asexual populations; (ii) are the response patterns similar in lethal and sublethal exposure conditions; and (iii) how does preexposure to cadmium influence these responses. No differences between the two species in mean acute tolerance (LC50) could be detected, but a significant difference was found between the slopes of the concentration-response curves. The steeper slope for P. antipodarum indicated a more uniform response for the asexual species than for H. ventrosa. In the sublethal experiment there was a significant difference in mean growth rate where, in general, P. antipodarum grew faster than H. ventrosa. P. antipodarum was more affected by cadmium at the low cadmium exposure, whereas growth rates were reduced equally for the two species at the high cadmium concentration. Pre-exposure to cadmium did not increase the tolerance to chronic exposure in either of the species, but P. antipodarum exhibited a tendency toward increased tolerance to acute cadmium stress after pre-exposure.The results show that there are differences between these closely related sexual and asexual species in response to cadmium, and that these differences are more pronounced under chronic sublethal exposure conditions.