Kent B. Woodburn

Ecotoxicology of Chlorpyrifos

Chlorpyrifos is a broad-spectrum organophosphorothioate insecticide with a principal mechanism of toxicity by inactivation of acetylcholinesterase at nerve junctions. Unlike certain organochlorine pesticides, chlorpyrifos is relatively nonpersistent (Racke 1993), and its principal degradation products are less toxic than the parent chemical. Species sensitivity varies considerably across kingdom and phyla. In general, aquatic and terrestrial microorganisms and plants are tolerant to chlorpyrifos exposure. Aquatic invertebrates, particularly crustaceans and insect larvae, are sensitive to exposure: LC50s are generally less than 1 microgram/L, and no-observed-effect concentrations may be below 0.1 microgram/L in laboratory studies. Fish appear to be less sensitive, with LC50s generally between 1 and 100 micrograms/L and no-observed effect concentrations of approximately 0.5 microgram/L. In general, saltwater and freshwater organisms exhibit similar sensitivity to chlorpyrifos, considering the extreme phylogenetic and species differences in toxicity. Chlorpyrifos effects in aquatic ecosystems are complex because of the diversity of species assemblages and trophic interactions. In general, functional endpoints (e.g., community metabolism) are less sensitive than structural parameters of ecosystems (e.g., loss of sensitive species). Ecosystem recovery is dependent on the interaction of a variety of factors including treatment timing and application dose, rate of dissipation, species assemblages, trophic structure, and the reproductive capacity and growth rate of susceptible and tolerant populations. Terrestrial species are relatively tolerant of chlorpyrifos exposure, although contact toxicity to sensitive terrestrial invertebrates may occur at concentrations of 0.1 microgram/insect. Amphibians, birds, and mammals show similar sensitivity to orally administered chlorpyrifos, with LD50s ranging from 8 to > 400 mg/kg body weight. Long-term chronic feeding studies in birds and mammals have shown no observed effect concentrations to be greater than 1 mg/kg food. In general, field studies have shown limited or no acute toxicity to amphibians, reptiles, birds, or mammals.

A Weight of Evidence Analysis of the Chronic Ecotoxicity of Nonylphenol Ethoxylates, Nonylphenol Ether Carboxylates, and Nonylphenol

ABSTRACT Nonylphenol ethoxylates (NPE) are widely used surfactant compounds with many domestic and industrial applications. Due to the nature of their use in down-the-drain applications, spent NPE are discharged to septic systems or to wastewater treatment plants. Biodegradation of parent material during treatment is often incomplete, leading to release of NPE and their degradation intermediates into the environment. Considerable aquatic toxicity research has occurred on NPE and particularly on nonylphenol (NP). Available data were subjected to a quality review and all studies of acceptable quality were used in a weight of evidence hazard assessment. Data for NP were further analyzed using a Species Sensitivities Distribution (SSD) approach. About 90 chronic values are available (ChVs, geometric mean of the no-observed effect concentration and lowest-observed effect concentration for each endpoint reported), which may be reduced to average ChVs for each tested species. Higher mole NPE (NPE ≥ 9) had ChVs ranging from 900 to 14,100 μg/L, ChVs for the low mole nonylphenol ether carboxylate (NPEC1) ranged from 3200 to 12,000 μg/L, ChVs for lower mole NPE (NPE1,2) ranged from 11 to 500 μg/L, and ChVs for NP ranged from 5 to 3500 μg/L. Using the SSD analysis for NP with higher quality study results, the 10th percentile chronic effect value is 5.7 μg/L, which supports the draft USEPA criteria on NP of 5.9 μg/L.

A Weight of Evidence Approach to the Aquatic Hazard Assessment of Bisphenoi A

Bisphenol A (BPA; 4,4-isopropylidene diphenol) is a chemical intermediate used primarily in the production of epoxy resins and polycarbonate products. BPA has been identified in surface waters and, hence, has been the subject of considerable research into its potential effects on aquatic organisms. Available literature on the aquatic toxicity of BPA was reviewed for quality against European Union TGD and Organization of Economic Cooperation and Development GLP principles. From this review, studies of suitable quality covering numerous ecologically relevant endpoints were identified to evaluate the survival, growth, and reproductive success of aquatic organisms exposed to BPA. Those studies yielded approximately 70 no observed effect concentrations (ranging from 16 to 3640 μg/L) and lowest observed effect concentrations (160 to 11,000 μg/L) that were considered in this weight of evidence assessment. Across all data, adverse effects on survival, growth, and reproduction occurred only at concentrations of 160 μg/L and above. Secondary biochemical (e.g., vitellogenin induction) and morphological (e.g., gonad histology) data provide insight into mechanisms of action, but do not correlate with apical endpoints related to survival, growth, and reproduction. Comparing the weight of the evidence of the aquatic toxicity data that showed chronic effects at 160 μg/L and higher with typical surface water concentrations in the range of 0.001 to 0.10 μg/ L, BPA is unlikely to cause adverse effects on aquatic populations or ecosystems.

Workgroup report: review of fish bioaccumulation databases used to identify persistent, bioaccumulative, toxic substances.

Chemical management programs strive to protect human health and the environment by accurately identifying persistent, bioaccumulative, toxic substances and restricting their use in commerce. The advance of these programs is challenged by the reality that few empirical data are available for the tens of thousands of commercial substances that require evaluation. Therefore, most preliminary assessments rely on model predictions and data extrapolation. In November 2005, a workshop was held for experts from governments, industry, and academia to examine the availability and quality of in vivo fish bioconcentration and bioaccumulation data, and to propose steps to improve its prediction. The workshop focused on fish data because regulatory assessments predominantly focus on the bioconcentration of substances from water into fish, as measured using in vivo tests or predicted using computer models. In this article we review of the quantity, features, and public availability of bioconcentration, bioaccumulation, and biota–sediment accumulation data. The workshop revealed that there is significant overlap in the data contained within the various fish bioaccumulation data sources reviewed, and further, that no database contained all of the available fish bioaccumulation data. We believe that a majority of the available bioaccumulation data have been used in the development and testing of quantitative structure–activity relationships and computer models currently in use. Workshop recommendations included the publication of guidance on bioconcentration study quality, the combination of data from various sources to permit better access for modelers and assessors, and the review of chemical domains of existing models to identify areas for expansion.

Comparing laboratory and field measured bioaccumulation endpoints

An approach for comparing laboratory and field measures of bioaccumulation is presented to facilitate the interpretation of different sources of bioaccumulation data. Differences in numerical scales and units are eliminated by converting the data to dimensionless fugacity (or concentration-normalized) ratios. The approach expresses bioaccumulation metrics in terms of the equilibrium status of the chemical, with respect to a reference phase. When the fugacity ratios of the bioaccumulation metrics are plotted, the degree of variability within and across metrics is easily visualized for a given chemical because their numerical scales are the same for all endpoints. Fugacity ratios greater than 1 indicate an increase in chemical thermodynamic activity in organisms with respect to a reference phase (e.g., biomagnification). Fugacity ratios less than 1 indicate a decrease in chemical thermodynamic activity in organisms with respect to a reference phase (e.g., biodilution). This method provides a holistic, weight-of-evidence approach for assessing the biomagnification potential of individual chemicals because bioconcentration factors, bioaccumulation factors, biota-sediment accumulation factors, biomagnification factors, biota-suspended solids accumulation factors, and trophic magnification factors can be included in the evaluation. The approach is illustrated using a total 2393 measured data points from 171 reports, for 15 nonionic organic chemicals that were selected based on data availability, a range of physicochemical partitioning properties, and biotransformation rates. Laboratory and field fugacity ratios derived from the various bioaccumulation metrics were generally consistent in categorizing substances with respect to either an increased or decreased thermodynamic status in biota, i.e., biomagnification or biodilution, respectively. The proposed comparative bioaccumulation endpoint assessment method could therefore be considered for decision making in a chemicals management context.

Guidance for Evaluating In Vivo Fish Bioaccumulation Data

ABSTRACT Currently, the laboratory-derived fish bioconcentration factor (BCF) serves as one of the primary data sources used to assess the potential for a chemical to bioaccumulate. Consequently, fish BCF values serve a central role in decision making and provide the basis for development of quantitative structure–property relationships (QSPRs) used to predict the bioaccumulation potential of untested compounds. However, practical guidance for critically reviewing experimental BCF studies is limited. This lack of transparent guidance hinders improvement in predictive models and can lead to uninformed chemical management decisions. To address this concern, a multiple-stakeholder workshop of experts from government, industry, and academia was convened by the International Life Sciences Institute Health and Environmental Sciences Institute to examine the data availability and quality issues associated with in vivo fish bioconcentration and bioaccumulation data. This paper provides guidance for evaluating key aspects of study design and conduct that must be considered when judging the reliability and adequacy of reported laboratory bioaccumulation data. Key criteria identified for judging study reliability include 1) clear specification of test substance and fish species investigated, 2) analysis of test substance in both fish tissue and exposure medium, 3) no significant adverse effects on exposed test fish, and 4) a reported test BCF that reflects steady-state conditions with unambiguous units. This guidance is then applied to 2 data-rich chemicals (anthracene and 2,3,7,8-tetrachlorodibenzo-p-dioxin) to illustrate the critical need for applying a systematic data quality assessment process. Use of these guidelines will foster development of more accurate QSPR models, improve the performance and reporting of future laboratory studies, and strengthen the technical basis for bioaccumulation assessment in chemicals management.

Quantitative measurement of fathead minnow vitellogenin by liquid chromatography combined with tandem mass spectrometry using a signature peptide of vitellogenin.

Vitellogenin (VTG) has been proposed as a sensitive biomarker of exposure to environmental estrogenic contaminants that induce VTG production in oviparous species. Enzyme-linked immunosorbent assay (ELISA) methods are currently widely used to measure the VTG levels. In this paper, a new liquid chromatography combined with tandem mass spectrometry (LC/ESI-MS/MS) method for the quantitative analysis of VTG in the plasma of fathead minnows exposed to 17alpha-ethinylestradiol (EE2) has been developed. This method includes, first, the selection of the signature peptide, which involves sodium dodecyl sulfate-polyarylamide gel electrophoresis separation, in-gel digestion, LC/ESI-MS/MS analysis with an ion trap mass spectrometer, and sequence determination with the TurboSEQUEST MS/MS database application; second, optimization of the selected signature peptide in multireaction monitor (MRM) mode with a triple quadrupole mass spectrometer; and third, trypsin digestion of plasma and VTG quantitation via MRM-mode LC/ESI-MS/MS. A series of plasma samples from fathead minnows following exposure to EE2 was assayed. A good correlation was found when EE2-induced plasma samples from fathead minnows were analyzed with ELISA and the described new method. Although used here with fathead minnow, the new LC/ESI-MS/MS method could be easily applied to the analysis of VTG expressed in any other fish species. Quantitation of VTG by this method was found to be highly specific and linear. The absence of potential artifactual measurements of VTG at low exposure levels could also be critical in future studies that evaluate weakly estrogenic compounds in aquatic species.

Improving the quality and scientific understanding of trophic magnification factors (TMFs).

Magnification Factors (TMFs) Lawrence P. Burkhard,†,* Katrine Borga,̊‡ David E. Powell, Pim Leonards, Derek C. G. Muir, Thomas F. Parkerton, and Kent B. Woodburn †Mid-Continent Ecology Division, National Health and Environmental Effects Research Laboratory, Office of Research and Development, U.S. Environmental Protection Agency, 6201 Congdon Blvd, Duluth, Minnesota 55804, United States ‡Norwegian Institute for Water Research (NIVA), Oslo, Norway Dow Corning Corporation, Health and Environmental Sciences, Midland, Michigan 48640, United States Institute for Environmental Studies, VU University, The Netherlands Aquatic Contaminants Research Division, Water, Science, and Technology Directorate, Environment Canada, Burlington, Ontario, Canada ExxonMobil Biomedical Sciences, Houston, Texas 77002, United States

Decamethylcyclopentasiloxane (D5) environmental sources, fate, transport, and routes of exposure.

The environmental sources, fate, transport, and routes of exposure of decamethylcyclopentasiloxane (D5; CAS no. 541-02-6) are reviewed in the present study, with the objective of contributing to effective risk evaluation and assessment of this and related substances. The present review, which is part of a series of studies discussing aspects of an effective risk evaluation and assessment, was prompted in part by the findings of a Board of Review undertaken to comment on a decision by Environment Canada made in 2008 to subject D5 to regulation as a toxic substance. The present review focuses on the early stages of the assessment process and how information on D5s physical-chemical properties, uses, and fate in the environment can be integrated to give a quantitative description of fate and exposure that is consistent with available monitoring data. Emphasis is placed on long-range atmospheric transport and fate in water bodies receiving effluents from wastewater treatment plants (along with associated sediments) and soils receiving biosolids. The resulting exposure estimates form the basis for assessments of the resulting risk presented in other studies in this series. Recommendations are made for developing an improved process by which D5 and related substances can be evaluated effectively for risk to humans and the environment.

Comparing laboratory‐ and field‐measured biota–sediment accumulation factors

Standardized laboratory protocols for measuring the accumulation of chemicals from sediments are used in assessing new and existing chemicals, evaluating navigational dredging materials, and establishing site-specific biota-sediment accumulation factors (BSAFs) for contaminated sediment sites. The BSAFs resulting from the testing protocols provide insight into the behavior and risks associated with individual chemicals. In addition to laboratory measurement, BSAFs can also be calculated from field data, including samples from studies using in situ exposure chambers and caging studies. The objective of this report is to compare and evaluate paired laboratory and field measurement of BSAFs and to evaluate the extent of their agreement. The peer-reviewed literature was searched for studies that conducted laboratory and field measurements of chemical bioaccumulation using the same or taxonomically related organisms. In addition, numerous Superfund and contaminated sediment site study reports were examined for relevant data. A limited number of studies were identified with paired laboratory and field measurements of BSAFs. BSAF comparisons were made between field-collected oligochaetes and the laboratory test organism Lumbriculus variegatus and field-collected bivalves and the laboratory test organisms Macoma nasuta and Corbicula fluminea. Our analysis suggests that laboratory BSAFs for the oligochaete L. variegatus are typically within a factor of 2 of the BSAFs for field-collected oligochaetes. Bivalve study results also suggest that laboratory BSAFs can provide reasonable estimates of field BSAF values if certain precautions are taken, such as ensuring that steady-state values are compared and that extrapolation among bivalve species is conducted with caution.