Development and application of the SSD approach in scientific case studies for ecological risk assessment

Environmental benchmarks based on ecotoxicological assessment with planktonic species might not adequately protect benthic assemblages in lotic systems

Freshwater ecosystems face widespread diffuse and point-source contamination. Species Sensitivity Distributions (SSDs) have been used as a tool to determine chemical concentration benchmarks that represent protective levels for most species in the environment. Here we used a SSD approach to assess on the adequacy of standard planktonic organisms to reflect the response of benthic communities, critically supporting the structure and function of lotic ecosystems. For the purpose, SSDs reflecting non-lethal responses of standard planktonic and selected benthic organisms were built based on EC50 values (collected in the literature or estimated following testing herein) regarding three model contaminants: potassium dichromate (PD), 3,5-dichlorophenol (DCP) and lead chloride (LC). The derived HC5 estimates were discriminatory between chemicals and the uncertainty associated with the estimate was remarkably low. The HC5 estimates with corresponding uncertainty were generally within the same order of magnitude for the three chemicals tested, with better discrimination between chemicals regarding their hazardous potential being achieved for benthic organisms: DCP was clearly less hazardous than PD, but LC tends to be as hazardous as PD and DCP (assuming the confidence interval ranges). Moreover, benthic communities were more sensitive to both DCP and PD, in this later case the HC5 being lower by more than one order of magnitude than that found for planktonic communities; for LC, confidence intervals overlapped, preventing a feasible assumption regarding differential sensitivity of the compared communities. Microphytobenthos was highlighted as the most sensitive group to the three tested chemicals in SSDs covering the benthic compartment, while SSDs with planktonic organisms did not consistently show trends in sensitivity ordering. Overall, our results suggest that protective benchmarks retrieved from SSDs built with the responses of standard planktonic organisms (which are the most commonly used for regulation purposes) do not adequately protect benthic communities.

Advancing soil ecological risk assessments for petroleum hydrocarbon contaminated soils in Canada: Persistence, organic carbon normalization and relevance of species assemblages

Sediment toxicity studies and ecological risk assessments on organic contaminants routinely apply organic carbon normalization to toxicity data; however, no studies examine its potential for use in soils with petroleum hydrocarbon (PHC) contamination. Limited studies in soil ecotoxicology assess the influence of species assemblages used in species sensitivity distribution construction on the resulting guideline designated to of soil dwelling organisms. Canadian regulations utilize more conservative approaches to deriving guidelines with soil ecotoxicology data compared to the rest of the world, so we investigated the impact of these on soil invertebrates in a variety of field soils. In addition to toxicity, the persistence of a medium PHC mixture was also assessed in the field soils to determine the duration of toxic effects. We found organic matter influenced PHC toxicity to soil invertebrates, but persistence was influenced more by soil cation exchange capacity. Incorporating organic carbon normalization into species sensitivity distribution curves provided a higher level of protection to soil dwelling receptors in low organic matter soils as well as reduce the variability of PHC soil toxicity data. Soil remediation guidelines derived for protection of soil dwelling organisms using a diverse species assemblage provided similar levels of protection as guidelines developed with test species specific for remote, forested land uses in Canada. We conclude that: (i) Canadian hazard concentration values for PHC contamination of soils should be revisited as they may not be protective and (ii) that soil PHC guidelines for protection of soil dwelling organisms should be expressed as carbon normalized values.

Does intraspecific variability matter in ecological risk assessment? Investigation of genotypic variations in three macrophyte species exposed to copper

To limit anthropogenic impact on ecosystems, regulations have been implemented along with global awareness that human activities are harmful to the environment. Ecological risk assessment (ERA) is the main procedure which allows to assess potential impacts of stressors on the environment as a result of human activities. ERA is typically implemented through different steps of laboratory testing. The approaches taken for ERA evolve along with scientific knowledge, to improve predictions on ecological risks for ecosystems. We here address the importance of intraspecific variability as a potential source of error in the laboratory evaluation of pollutants. To answer this question, three aquatic macrophyte species with different life-history traits but with their leaves directly in contact with the water were chosen; Lemna minor and Myriophyllum spicatum, two OECD model species, and Ceratophyllum demersum. For each species, three or four genotypes were exposed to 7-8 copper concentrations (up to 1.9 mg/L, 2 mg/L or 36 mg/L for C. demersum, L. minor and M. spicatum, respectively). To assess species sensitivity, growth-related endpoints such as Relative Growth Rate (RGR), based either on biomass production or on length/frond production, and chlorophyll fluorescence F_v/F_m, were measured. For each endpoint, the effective concentration 50% (EC₅₀) was calculated. Almost all endpoints were affected by Cu exposure, except F_v/F_m of M. spicatum, and resulted in significant differences among genotypes for Cu sensitivity. Genotypes of L. minor exhibited up to 35% of variation in EC50 values based on F_v/F_m, showing differential sensivity among genotypes. Significant differences in EC₅₀ values were found for RGR based on length for M. spicatum, with up to 72% of variation. Finally, C. demersum demonstrated significant sensitivity differences among genotypes with up to 78% variation for EC₅₀ based on length. Overall, interspecific variation was higher than intraspecific variation, and explained 77% of the variation found among genotypes for RGR based on biomass, and 99% of the variation found for F_v/F_m. Our results highlight that depending on the endpoint, sensitivity can vary greatly within a species, and that pollutant- and species-specific endpoints should be considered in ERA.

Prioritizing anthropogenic chemicals in drinking water and sources through combined use of mass spectrometry and ToxCast toxicity data

Advancements in high-resolution mass spectrometry based methods have enabled a shift from pure target analysis to target, suspect and non-target screening analyses to detect chemicals in water samples. The multitude of suspect chemicals thereby detected needs to be prioritized for further identification, prior to health risk assessment and potential inclusion into monitoring programs. Here, we compare prioritization of chemicals in Dutch water samples based on relative intensities only to prioritization including hazard information based on high-throughput in vitro toxicity data. Over 1000 suspects detected in sewage treatment plant effluent, surface water, groundwater and drinking water samples were ranked based on their relative intensities. Toxicity data availability and density in the ToxCast database were determined and visualized for these suspects, also in regard to water relevant mechanisms of toxicity. More than 500 suspects could be ranked using occurrence/hazard ratios based on more than 1000 different assay endpoints. The comparison showed that different prioritization strategies resulted in significantly different ranking, with only 2 suspects prioritized based on occurrence among the top 20 in the hazard ranking. We therefore propose a novel scheme that integrates both exposure and hazard data, and efficiently prioritizes which features need to be confidently identified first.

How do we take the pulse of an aquatic ecosystem? Current and historical approaches to measuring ecosystem integrity

Global environmental monitoring has indicated that the structure and function of some aquatic ecosystems has been significantly altered by human activities. There are many potential causes for these changes; however, one major concern is the increasing release of anthropogenic contaminants into aquatic environments. Although toxicological responses of individual organisms are typically well characterized, few studies have focused on characterizing toxicity at the ecosystem level. In fact, because of their scale and complexity, changes in ecosystem integrity are rarely considered in assessments of risks to ecosystems. This work attempts to move the conversation forward by defining integrity of ecosystems, reviewing current and historical approaches to measuring ecosystem integrity status (e.g., structural and functional measurements), and highlighting methods that could significantly contribute to the field of ecosystem toxicology (e.g., keystone species, environmental energetics, ecotoxicological modeling, and adverse outcome pathways [AOPs]). Through a critical analysis of current and historical methodologies, the present study offers a comprehensive, conceptual framework for the assessment of risks of contaminant exposure for whole ecosystems and proposes steps to facilitate better diagnoses of the integrity of aquatic systems. Environ Toxicol Chem 2019;38:289-301. © 2018 SETAC.

Risk assessment of agriculture impact on the Frío River watershed and Caño Negro Ramsar wetland, Costa Rica

The Caño Negro Ramsar wetland is a conservation area of great natural and societal value, located in the lower part of the Frío River watershed in the north of Costa Rica. Its aquatic ecosystems may be considered vulnerable to pollution due to recent changes in land use toward agriculture. In 2011 and 2012, quarterly sampling was done at ten sites located in the middle and lower sections of the Frío River Basin that pass through crop areas and later drain into Caño Negro wetland. Pesticide residues, nitrates, sediment concentrations, and diversity of benthic macroinvertebrates and fish biomarkers were studied in the selected sites. Additionally, risk of toxicity was calculated in two different ways: (1) by using a ratio of MEC to hazard concentrations threshold for 5% of species (HC₅) to calculate a risk quotient (RQ), and (2) by using a ratio of MEC to available ecotoxicity data of native fish and cladocera for diazinon and ethoprophos, to obtain a risk quotient for native species (RQns). Results indicated that three out of the ten sites (rivers Thiales, Mónico, and Sabogal) showed variable levels of pollution including six different active ingredients (a.i.) of pesticide formulations (herbicides ametryn, bromacil, and diuron; insecticides cypermethrin, diazinon, and ethoprophos). Moreover, potential adverse effects on fishes in Thiales and Mónico rivers were indicated by cholinesterase (ChE) inhibition and glutathione S-transferase (GST) enhancement. Risk evaluations indicated pesticide residues of ametryn, bromacil, and ethoprophos to be exceeding the limits set by MTR, also RQ was high (>1) in 70% of the positive samples for diuron (most frequently found pesticide in water samples), cypermethrin, diazinon, and ethoprophos, and RQns was high for diazinon. Therefore, these substances might be of major concern for the ecological health of aquatic ecosystems in the middle basin of the Frío River. The most critical site was Mónico River, which had the highest pollution (75% detection samples with 3-5 a.i.) and highest calculated risk (RQ > 1 in 75% of the samples). This is also the river that most directly drains into the protected wetland. Even though pesticide pollution in this area is not as severe as in other parts of Costa Rica, it is imperative that measures are taken, particularly in the surroundings of Mónico River, in order to diminish and mitigate possible detrimental effects to biota in Caño Negro Ramsar Site.

Life-cycle studies with 2 marine species and bisphenol A: The mysid shrimp (Americamysis bahia) and sheepshead minnow (Cyprinodon variegatus)

Bisphenol A (BPA) is a high production volume compound primarily used to produce epoxy resins and polycarbonate plastic. Exposure to low concentrations of BPA occurs in freshwater and marine systems, primarily from wastewater treatment plant discharges. The dataset for chronic toxicity of BPA to freshwater organisms includes studies on fish, amphibians, invertebrates, algae, and aquatic plants. To broaden the dataset, a 1.5-generation test with sheepshead minnow (Cyprinodon variegatus) and a full life-cycle test with mysid shrimp (Americamysis bahia) were conducted. Testing focused on apical endpoints of survival, growth and development, and reproduction. The respective no-observed-effect concentration (NOEC) and lowest-observed-effect concentration (LOEC) values of 170 and 370 µg/L for mysid and 66 and 130 μg/L for sheepshead were based on reduced fecundity. The hazardous concentrations for 5% of the species (HC5) values of 18 μg/L were calculated from species sensitivity distributions (SSDs) with freshwater-only data and combined freshwater and marine data. Inclusion of marine data resulted in no apparent difference in SSD shape, R² values for the distributions, or HC5 values. Upper-bound 95th percentile concentrations of BPA measured in marine waters of North America and Europe (0.024 and 0.15 μg/L, respectively) are below the HC5 value of 18 μg/L. These results suggest that marine and freshwater species are of generally similar sensitivity and that chronic studies using a diverse set of species can be combined to assess the aquatic toxicity of BPA. Environ Toxicol Chem 2018;37:398-410. © 2017 The Authors. Environmental Toxicology and Chemistry Published by Wiley Periodicals, Inc. on behalf of SETAC.

Applying adverse outcome pathways and species sensitivity-weighted distribution to predicted-no-effect concentration derivation and quantitative ecological risk assessment for bisphenol A and 4-nonylphenol in aquatic environments: A case study on Tianjin City, China

Adverse outcome pathways (AOPs) are a novel concept that effectively considers the toxic modes of action and guides the ecological risk assessment of chemicals. To better use toxicity data including biochemical or molecular responses and mechanistic data, we further developed a species sensitivity-weighted distribution (SSWD) method for bisphenol A and 4-nonylphenol. Their aquatic predicted-no-effect concentrations (PNECs) were derived using the log-normal statistical extrapolation method. We calculated aquatic PNECs of bisphenol A and 4-nonylphenol with values of 4.01 and 0.721 µg/L, respectively. The ecological risk of each chemical in different aquatic environments near Tianjin, China, a coastal municipality along the Bohai Sea, was characterized by hazard quotient and probabilistic risk quotient assessment techniques. Hazard quotients of 7.02 and 5.99 at 2 municipal sewage sites using all of the endpoints were observed for 4-nonylphenol, which indicated high ecological risks posed by 4-nonylphenol to aquatic organisms, especially endocrine-disrupting effects. Moreover, a high ecological risk of 4-nonylphenol was indicated based on the probabilistic risk quotient method. The present results show that combining the SSWD method and the AOP concept could better protect aquatic organisms from adverse effects such as endocrine disruption and could decrease uncertainty in ecological risk assessment. Environ Toxicol Chem 2018;37:551-562. © 2017 SETAC.

Review: ecotoxicity of organic and organo-metallic antifouling co-biocides and implications for environmental hazard and risk assessments in aquatic ecosystems

Hazard assessments of Irgarol 1051, diuron, 2-(thiocyanomethylthio)benzothiazole (TCMTB), dichloro-octylisothiazolin (DCOIT), chlorothalonil, dichlofluanid, thiram, zinc pyrithione, copper pyrithione, triphenylborane pyridine (TPBP), capsaicin, nonivamide, tralopyril and medetomidine were performed to establish robust environmental quality standards (EQS), based on predicted no effect concentrations (PNECs). Microalgae, zooplankton, fish and amphibians were the most sensitive ecological groups to all the antifoulants evaluated, especially in the early life stages. No differences were identified between freshwater and seawater species. The use of toxicity tests with non-standard species is encouraged because they increase the datasets, allowing EQS to be derived from probabilistic-based PNECs whilst reducing uncertainties. The global ban of tributyltin (TBT) has been heralded as a major environmental success; however, substitute antifoulants may also pose risks to aquatic ecosystems. Environmental risk assessments (ERAs) have driven decision-makings for regulating antifouling products, but in many countries there is still a lack of regulation of antifouling biocides which should be addressed.

Future needs and recommendations in the development of species sensitivity distributions: Estimating toxicity thresholds for aquatic ecological communities and assessing impacts of chemical exposures

A species sensitivity distribution (SSD) is a probability model of the variation of species sensitivities to a stressor, in particular chemical exposure. The SSD approach has been used as a decision support tool in environmental protection and management since the 1980s, and the ecotoxicological, statistical, and regulatory basis and applications continue to evolve. This article summarizes the findings of a 2014 workshop held by the European Centre for Toxicology and Ecotoxicology of Chemicals and the UK Environment Agency in Amsterdam, The Netherlands, on the ecological relevance, statistical basis, and regulatory applications of SSDs. An array of research recommendations categorized under the topical areas of use of SSDs, ecological considerations, guideline considerations, method development and validation, toxicity data, mechanistic understanding, and uncertainty were identified and prioritized. A rationale for the most critical research needs identified in the workshop is provided. The workshop reviewed the technical basis and historical development and application of SSDs, described approaches to estimating generic and scenario-specific SSD-based thresholds, evaluated utility and application of SSDs as diagnostic tools, and presented new statistical approaches to formulate SSDs. Collectively, these address many of the research needs to expand and improve their application. The highest priority work, from a pragmatic regulatory point of view, is to develop a guidance of best practices that could act as a basis for global harmonization and discussions regarding the SSD methodology and tools. Integr Environ Assess Manag 2017;13:664-674. © 2016 SETAC.

The Consequences of Nonrandomness in Species-Sensitivity in Relation to Functional Traits for Ecosystem-Level Effects of Chemicals

Estimating ecosystem-level effects from single-species bioassays is a major challenge in environmental risk assessment. Most extrapolation procedures are based on the implicit assumption that species sensitivities are random with regard to their functional traits. Here, we explore how nonrandomness in species sensitivities affects how species-level and ecosystem level effects of chemical exposure correspond. The effect of a correlation between the trait value under control conditions and the sensitivity of the trait to chemical stress is studied for two traits (per capita growth rate and monoculture yield) under constant and temporary exposure. Theoretical model predictions are thereby validated against a 3-week microcosm experiment, in which eight marine diatoms systems with different correlations between trait values and sensitivities were temporary (1 week) or constantly (3 weeks) exposed to two concentrations of the herbicide atrazine (100 and 250 μg L^-1). Negative correlations increased the reduction in ecosystem functioning (productivity) by atrazine for both traits. However, correlations in the per capita growth rate affected productivity only shortly following changes in environmental conditions, whereas correlations in the monoculture yield affected productivity throughout exposure. Correlations between species sensitivities and functional trait values can thus help to identify when ecosystem-level effects are likely to exceed species-level effects.

III: Use of biomarkers as Risk Indicators in Environmental Risk Assessment of oil based discharges offshore

Offshore oil and gas activities are required not to cause adverse environmental effects, and risk based management has been established to meet environmental standards. In some risk assessment schemes, Risk Indicators (RIs) are parameters to monitor the development of risk affecting factors. RIs have not yet been established in the Environmental Risk Assessment procedures for management of oil based discharges offshore. This paper evaluates the usefulness of biomarkers as RIs, based on their properties, existing laboratory biomarker data and assessment methods. Data shows several correlations between oil concentrations and biomarker responses, and assessment principles exist that qualify biomarkers for integration into risk procedures. Different ways that these existing biomarkers and methods can be applied as RIs in a probabilistic risk assessment system when linked with whole organism responses are discussed. This can be a useful approach to integrate biomarkers into probabilistic risk assessment related to oil based discharges, representing a potential supplement to information that biomarkers already provide about environmental impact and risk related to these kind of discharges.

II. Species sensitivity distributions based on biomarkers and whole organism responses for integrated impact and risk assessment criteria

The aim of this paper is to bridge gaps between biomarker and whole organism responses related to oil based offshore discharges. These biomarker bridges will facilitate acceptance criteria for biomarker data linked to environmental risk assessment and translate biomarker results to higher order effects. Biomarker based species sensitivity distributions (SSD_biomarkers) have been constructed for relevant groups of biomarkers based on laboratory data from oil exposures. SSD curves express the fraction of species responding to different types of biomarkers. They have been connected to SSDs for whole organism responses (WORs) constructed in order to relate the SSD_biomarkers to animal fitness parameters that are commonly used in environmental risk assessment. The resulting SSD curves show that biomarkers and WORs can be linked through their potentially affected fraction of species (PAF) distributions, enhancing the capability to monitor field parameters with better correlation to impact and risk assessment criteria and providing improved chemical/biological integration.

Determination and validation of an aquatic Maximum Acceptable Concentration-Environmental Quality Standard (MAC-EQS) value for the agricultural fungicide azoxystrobin

The main goal of the present study was to determine and validate an aquatic Maximum Acceptable Concentration-Environmental Quality Standard (MAC-EQS) value for the agricultural fungicide azoxystrobin (AZX). Assessment factors were applied to short-term toxicity data using the lowest EC₅₀ and after the Species Sensitivity Distribution (SSD) method. Both ways of EQS generation were applied to a freshwater toxicity dataset for AZX based on available data, and to marine toxicity datasets for AZX and Ortiva^® (a commercial formulation of AZX) obtained by the present study. A high interspecific variability in AZX sensitivity was observed in all datasets, being the copepoda Eudiaptomus graciloides (LC_50,48h = 38 μg L^-1) and the gastropod Gibbula umbilicalis (LC_50,96h = 13 μg L^-1) the most sensitive freshwater and marine species, respectively. MAC-EQS values derived using the lowest EC₅₀ (≤0.38 μg L^-1) were more protective than those derived using the SSD method (≤3.2 μg L^-1). After comparing the MAC-EQS values estimated in the present study to the smallest AA-EQS available, which protect against the occurrence of prolonged exposure of AZX, the MAC-EQS values derived using the lowest EC₅₀ were considered overprotective and a MAC-EQS of 1.8 μg L^-1 was validated and recommended for AZX for the water column. This value was derived from marine toxicity data, which highlights the importance of testing marine organisms. Moreover, Ortiva affects the most sensitive marine species to a greater extent than AZX, and marine species are more sensitive than freshwater species to AZX. A risk characterization ratio higher than one allowed to conclude that AZX might pose a high risk to the aquatic environment. Also, in a wider conclusion, before new pesticides are approved, we suggest to improve the Tier 1 prospective Ecological Risk Assessment by increasing the number of short-term data, and apply the SSD approach, in order to ensure the safety of aquatic organisms.