F. De Laender

Non-simultaneous ecotoxicity testing of single chemicals and their mixture results in erroneous conclusions about the joint action of the mixture

The ecotoxicity of binary chemical mixtures with a common mode of action is often predicted with the concentration addition model. The assumption of concentration addition is commonly tested statistically based on results of toxicity experiments with the two single chemicals and their binary mixture. The present simulation study shows that if not all these experiments are performed simultaneously, one has a 20-80% chance of concluding synergism or antagonism while the mixture is actually additive (false positive rate). Truly synergistic or antagonistic mixtures have a 10-50% chance of being falsely categorized as additive (false negative rate). Additionally, false positive rates decrease with increasing experimental error, while false negative rates increase with increasing experimental error. Based on these results, we put forward a number of recommendations for future mixture ecotoxicity evaluation.

Combining Monitoring Data and Modeling Identifies PAHs as Emerging Contaminants in the Arctic

Protecting Arctic ecosystems against potential adverse effects from anthropogenic activities is recognized as a top priority. In particular, understanding the accumulation and effects of persistent organic pollutants (POPs) in these otherwise pristine ecosystems remains a scientific challenge. Here, we combine more than 20,000 tissue concentrations, a food web bioaccumulation model, and time trend analyses to demonstrate that the concentrations of legacy-POPs in the Barents/Norwegian Sea fauna decreased 10-fold between 1985 and 2010, which reflects regulatory efforts to restrict these substances. In contrast, concentrations of fossil fuel derived PAHs in lower trophic levels (invertebrates and fish) increased 10 to 30 fold over the past 25 years and now dominate the summed POP burden (25 POPs, including 11 PAHs) in these biota. Before 2000, PCBs dominated the summed POP burden in top predators. Our findings indicate that the debate on the environmental impacts of fossil fuel burning should move beyond the expected seawater temperature increase and examine the possible environmental impact of fossil fuel derived PAHs.

Theoretically exploring direct and indirect chemical effects across ecological and exposure scenarios using mechanistic fate and effects modelling

Predicting ecosystem response to chemicals is a complex problem in ecotoxicology and a challenge for risk assessors. The variables potentially influencing chemical fate and exposure define the exposure scenario while the variables determining effects at the ecosystem level define the ecological scenario. In absence of any empirical data, the objective of this paper is to present simulations by a fugacity-based fate model and a differential equation-based ecosystem model to theoretically explore how direct and indirect effects on invertebrate shallow pond communities vary with changing ecological and exposure scenarios. These simulations suggest that direct and indirect effects are larger in mesotrophic systems than in oligotrophic systems. In both trophic states, interaction strength (quantified using grazing rates) was suggested a more important driver for the size and recovery from direct and indirect effects than immigration rate. In general, weak interactions led to smaller direct and indirect effects. For chemicals targeting mesozooplankton only, indirect effects were common in (simple) food-chains but rare in (complex) food-webs. For chemicals directly affecting microzooplankton, the dominant zooplankton group in the modelled community, indirect effects occurred both in food-chains and food-webs. We conclude that the choice of the ecological and exposure scenarios in ecotoxicological modelling efforts needs to be justified because of its influence on the prevalence and magnitude of the predicted effects. Overall, more work needs to be done to empirically test the theoretical expectations formulated here.

Toxicity data for modeling impacts of oil components in an Arctic ecosystem.

Ecological impact assessment modeling systems are valuable support tools for managing impacts from commercial activities on marine habitats and species. The inclusion of toxic effects modeling in these systems is predicated on the availability and quality of ecotoxicology data. Here we report on a data gathering exercise to obtain toxic effects data on oil compounds for a selection of cold-water marine species of fish and plankton associated with the Barents Sea ecosystem. Effects data were collated from historical and contemporary literature resources for the endpoints mortality, development, growth, bioaccumulation and reproduction. Evaluating the utility and applicability of these data for modeling, we find that data coverage is limited to a sub-set of the required endpoints. There is a need for new experimental studies for zooplankton focused on the endpoints development and bioaccumulation and for larvae and juvenile fish focused on growth and development.

Uncertainties in ecological, chemical and physiological parameters of a bioaccumulation model: implications for internal concentrations and tissue based risk quotients.

Bioaccumulation models predict internal contaminant concentrations (c(i)) using ecological, chemical and physiological parameters. Here we analyse the effect of uncertainties on these parameters on bioaccumulation model predictions. Simultaneously considering the uncertainties on all these parameters in a bioaccumulation model resulted in uncertainty ranges of c(i) that increased with the octanol water partition coefficient K(ow) and reached maxima of up to 1.25 log units for mesozooplankton and up to 1.45 log units fish at logK(ow)=8. A global sensitivity analysis (SA) was performed to rank the contribution of different parameters to the observed uncertainty. The SA demonstrated that this interspecies difference resulted predominantly from uncertain production rates of fish. The K(ow), the water concentration and organic carbon-octanol proportionality constant were important drivers of uncertainty on c(i) for both species. A tissue based risk quotient (RQ(tissue)) combining uncertainty on c(i) with realistic tissue based effect thresholds indicated that fish were up to 10 times more probable to have RQ(tissue)>1 than mesozooplankton, depending on the considered threshold value. Conventional exposure based risk quotients were up to 5 times less probable to exceed one than were corresponding RQ(tissue), and this for both species.

Functional redundancy and food web functioning in linuron-exposed ecosystems

An extensive data set describing effects of the herbicide linuron on macrophyte-dominated microcosms was analysed with a food web model to assess effects on ecosystem functioning. We showed that sensitive phytoplankton and periphyton groups in the diets of heterotrophs were gradually replaced by more tolerant phytoplankton species as linuron concentrations increased. This diet shift--showing redundancy among phytoplankton species--allowed heterotrophs to maintain their functions in the contaminated microcosms. On an ecosystem level, total gross primary production was up to hundred times lower in the treated microcosms but the uptake of dissolved organic carbon by bacteria and mixotrophs was less sensitive. Food web efficiency was not consistently lower in the treated microcosms. We conclude that linuron predominantly affected the macrophytes but did not alter the overall functioning of the surrounding planktonic food web. Therefore, a risk assessment that protects macrophyte growth also protects the functioning of macrophyte-dominated microcosms.

Migration and opportunistic feeding increase PCB accumulation in Arctic seabirds

It is widely accepted that body concentrations of persistent organic pollutants (POPs) tend to increase with trophic level (TL). Yet, little attention has been paid to the causes in the underlying differences in POP body concentrations between species occupying similar TLs. In this paper we use two modeling approaches to quantify the importance of migration and opportunistic feeding, relative to that of trophic level, in explaining interspecific differences in polychlorinated biphenyl (PCB) body concentrations between 6 Arctic seabird species breeding in the Barents Sea: Little Auk (Alle alle), Black Guillemot (Cepphus grylle), Brünnichs Guillemot (Uria lomvia), Common Eider (Somateria mollissima), Black-legged Kittiwake (Rissa tridactyla), and Glaucous Gull (Larus hyperboreus). As a first approach, we use additive models to analyze two independent data sets (n = 470 and n = 726). We demonstrate that migration, opportunistic feeding, and TL significantly (p < 0.001) increase PCB body concentrations by a factor 3.61-4.10, 2.66-20.95, and 2.38-2.41, respectively. Our second approach, using a mechanistic bioaccumulation model, confirmed these positive effects on the body burdens but suggested lower effects of migration, opportunistic feeding, and TL (1.55, 2.39, and 2.38) than did our statistical analysis. These two independent approaches demonstrate that the effects of migration and opportunistic feeding on seabird body burdens can be similar to that of an increase of one TL and should therefore be accounted for in future analyses.

Simulation of Spatial and Temporal Variability of Chronic Copper Toxicity to Daphnia magna and Pseudokirchneriella subcapitata in Swedish and British Surface Waters

ABSTRACT Water Quality Criteria (WQC) for metals are usually based on single species laboratory toxicity data. The influence of water characteristics of the surface waters on bioavailability to freshwater organisms is hence neglected, along with regional and temporal variability of these water characteristics. A methodology is presented to account for regional and temporal variability in the WQC setting for copper in the United Kingdom and Sweden. Bioavailability models were applied in a Monte-Carlo approach to account for temporal variability and a Geographic Information System was used to account for geographical variability on the chronic copper toxicity to Daphnia magna and Pseudokirchneriella subcapitata. Fifth percentiles of distributions of the No Observed Effect Concentration (NOEC) for both model species were derived in both study regions. For P. subcapitata, it was demonstrated that this fifth percentile can vary by a factor 10 in the UK study region. The ratio of these NOEC fifth percentiles (D. magna percentile divided by P. subcapitata percentile) was used to compare the ecotoxicity of copper to two model species. This ratio showed the highest variability (a factor 5) within the Swedish study region. The findings of this research stress the need for the use of region-specific WQC for copper.

Using additive modelling to quantify the effect of chemicals on phytoplankton diversity and biomass

Environmental authorities require the protection of biodiversity and other ecosystem properties such as biomass production. However, the endpoints listed in available ecotoxicological datasets generally do not contain these two ecosystem descriptors. Inferring the effects of chemicals on such descriptors from micro- or mesocosm experiments is often hampered by inherent differences in the initial biodiversity levels between experimental units or by delayed community responses. Here we introduce additive modelling to establish the effects of a chronic application of the herbicide linuron on 10 biodiversity indices and phytoplankton biomass in microcosms. We found that communities with a low (high) initial biodiversity subsequently became more (less) diverse, indicating an equilibrium biodiversity status in the communities considered here. Linuron adversely affected richness and evenness while dominance increased but no biodiversity indices were different from the control treatment at linuron concentrations below 2.4 μg/L. Richness-related indices changed at lower linuron concentrations (effects noticeable from 2.4 μg/L) than other biodiversity indices (effects noticeable from 14.4 μg/L) and, in contrast to the other indices, showed no signs of recovery following chronic exposure. Phytoplankton biomass was unaffected by linuron due to functional redundancy within the phytoplankton community. Comparing thresholds for biodiversity with conventional toxicity test results showed that standard ecological risk assessments also protect biodiversity in the case of linuron.

The ChimERA project: Coupling mechanistic exposure and effect models into an integrated platform for ecological risk assessment

Current techniques for the ecological risk assessment of chemical substances are often criticised for their lack of environmental realism, ecological relevance and methodological accuracy. ChimERA is a 3-year project (2013–2016), funded by Cefic’s Long Range Initiative (LRI) that aims to address some of these concerns by developing and testing mechanistic fate and effect models, and coupling of these models into one integrated platform for risk assessment. This paper discusses the backdrop against which this project was initiated and lists its objectives and planned methodology.