Fathead minnows (Pimephales promelas) were exposed to 17 μg Cu∙L−1 or 6 μg Cd∙L−1 in synthetic soft water in the presence of competing ligands. Measured gill metal concentrations correlated with free metal ion concentrations, not with total metal. Langmuir isotherms were used to calculate conditional metal–gill equilibrium constants and the number of binding sites for each metal. Log KCu-gill was estimated to be 7.4 and the number of Cu binding sites on a set of gills (70 mg, wet weight) was ~2 × 10−10 mol (~30 nmol∙g wet weight−1). Log KCd-gill was ~8.6, and the number of Cd binding sites on minnow gills was ~2 × 10−10 mol (~2 nmol∙g wet weight−1). Stability constants for H+ and Ca interactions at metal–gill binding sites and for metal interactions with dissolved organic carbon (DOC) were estimated using these metal–gill constants. All stability constants were entered into the MSNEQL+ aquatic chemistry program, to predict metal accumulation on fish gills using metal, DOC, and Ca concentrations, and water pH. Calculated metal accumulation on gills correlated well with measured gill metal concentrations and with LC50 values. Our approach of inserting biological data into an aquatic chemistry program is useful for modelling and predicting metal accumulation on gills and therefore toxicity to fish.

Adult fathead minnows (Pimephales promelas) were exposed to 17 g Cu∙L−1 or 6 g Cd∙L−1 for 2 to 3 h in synthetic softwater solutions at pH 6.2 containing either naturally-occurring, freeze-dried dissolved organic carbon (DOC) or synthetic ligands such as EDTA. After exposures, gills were assayed for bound Cu or Cd. As a first approximation, lake of origin or molecular size fraction of DOC did not influence Cu binding to gills, while DOC concentration did. DOC concentrations ≥4.8 mg∙L−1 prevented Cu from accumulating on fathead gills. At the relatively low concentrations used, neither Cu nor Cd interfered with binding of the other metal on gills, suggesting different gill binding sites. Cadmium accumulation on gills was more sensitive to increased concentrations of Ca and H+ than was Cu. Surprisingly, Cd bound to gills to the same or greater extent than did Cu: for synthetic ligands, Cd binds less well than Cu. This result corroborates previously published observations that Cd, unlike Cu, is taken up at gills through high affinity Ca channels. Accumulation of Cd on fish gills was never associated with 14C-labelled EDTA or 14C-citrate, indicating that free metal interacts with the gill while metal–ligand complexes usually do not.

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Formaldehyde is one of the shortlist substances permitted for use in aquaculture. Toxicity of formaldehyde and therapeutical success is influenced by water parameters. However, there is a lack of information on the interaction of organic carbon and calcium (Ca 2+ ) on the toxicity of formaldehyde. Laboratory experiments were conducted to test the combined effects of Ca 2+ and natural organic matter (NOM) on formaldehyde toxicity. Zebrafish embryos were exposed to five concentrations of formaldehyde for 144 h. Juveniles exposed to high concentrations died; the embryos exposed to low concentrations were unable to hatch, particularly visible in the groups without NOM. The toxicity-reducing effects of NOM are not attributable to the presence of Ca 2+ .

A number of biological responses and multigenerational effects, mediated through the disruption of endocrine systems, have been observed in biota exposed to relatively low concentrations of environmental contaminants. These types of responses need to be considered within a weight of evidence approach in our risk assessment and risk management frameworks. However, including endocrine responses in an environmental risk assessment introduces a number of uncertainties that must be considered. A risk assessment of nonylphenol and nonylphenol polyethoxylates (NP/NPE) is used as a case study to demonstrate the sources and magnitude of some of the uncertainties associated with using endocrine disruption as an assessment endpoint. Even with this relatively well studied group of substances, there are substantial knowledge gaps which contribute to the overall uncertainties, limiting the interpretation within the risk assessment. The uncertainty of extrapolating from in vitro or biochemical responses to higher levels of organization or across species is not well understood. The endocrine system is very complex and chemicals can interact or interfere with the normal function of endocrine systems in a number of ways (e.g., receptors, hormones) which may or may not result in an adverse responses in the whole organism. Using endocrine responses can lead to different conclusions than traditional endpoints due to a variety of factors, such as differences in relative potencies of chemicals for specific endpoints (e.g., receptor binding versus chronic toxicity). The uncertainties can also be considerably larger and the desirability of using endocrine endpoints should be carefully evaluated. Endocrine disruption is a mode of action and not a functional endpoint and this needs to be considered carefully in the problem formulation stage and the interpretation of the weight of evidence.

Biosolids and animal wastes can contain natural hormones or synthetic chemicals that have the potential to disrupt endocrine function in wildlife should they move offsite. The persistence in soil of estrogenic substances that could reach agricultural land via fertilization with organic amendments has been evaluated. 4-Nonylphenol, ethynylestradiol, estradiol, and estrone are rapidly dissipated in soils under a range of conditions typical of a temperate growing season with half-lives ranging from a few hours to a few days. We conclude that these chemicals are rapidly removed from aerated soils under temperate growing conditions such that application methods that minimize preferential flow or runoff of animal or human wastes should protect adjacent water from contamination. The use of recombinant yeast and cell culture estrogen receptor gene transcription bioassays were investigated as potential tools to detect non-labile estrogenic or anti-estrogenic substances in runoff from soils receiving liquid swine slurry or biosolids. Key words: biosolids, manures, endocrine disruption, estrogen, nonylphenol, soil persistence, bioassay.