Bioaccumulation is an important information requirement for chemicals risk assessment. The most widely used test guideline for measuring bioaccumulation in fish is the OECD 305 test guideline and, in the future, it is likely to include a dietary exposure method for substances that are difficult to test by the more usual aqueous exposure route. This new method results in a biomagnification factor (BMF), whereas for regulatory purposes a bioconcentration factor (BCF) is often required. Therefore, being able to estimate a BCF quantitatively from the data generated in the dietary study would meet an accepted regulatory need. The information generated by the dietary study includes the depuration rate constant. To use these data to estimate a BCF, an estimate of the rate constant for uptake from water is needed, allowing a kinetic BCF to be calculated. The present study considers and tests methods that are currently available for predicting uptake rate constants from water using a database of bioconcentration data. A number of methods were found to perform similarly when tested with substances with a log K(OW) range of approximately 3.5 to 8.2. The uncertainty in the estimated uptake rate constant was relatively large, however, even for the best performing methods.
No physicochemical parameter in environmental toxicology and chemistry is better known than K OW , the octanol-water partition coefficient. This parameter, also called log P or log P oct , originates from research into quantitative structureactivity relationships (QSARs) [1]. The first studies were from Corwin Hansch and were focused on optimizing the biological as well as the pharmacological activity of chemicals. The coefficient K OW is a measure of hydrophobicity, and several processes, including sorption and accumulation, are driven by hydrophobicity. It is the key parameter for environmental fate and exposure modeling programs [2]. An ecological risk assessment for organic compounds without consideration of its K OW value seems impossible. Also, as an input parameter in QSARs, K OW is dominant. Guidance documents for risk assessment of existing chemicals list numerous models for the prediction of bioconcentration factors, soil sorption, and sorption to dissolved organic carbon that are all based on K OW [3]. Classic examples are QSARs for prediction of soil sorption [4], bioaccumulation [5,6], and baseline toxicity [7]. A clear example of the strength of K OW as a parameter is in the development of models for the prediction of quality criteria for chemicals that act via narcosis. Here, predictions of effect concentrations, bioconcentration factors, and sediment sorption from K OW are combined into one overall model [8,9]. Several papers in the "Top 100" show examples of methods for estimating parameters from octanol-water partition coefficients, including the estimation of aqueous solubility [10] and bioconcentration factors [11].While K OW itself is a simple parameter, measurement is not so straightforward. A hydrophobic chemical is dissolved in octanol in a shake flask or a glass vial, and water is added. The system is shaken until equilibrium, and the concentrations are measured in both phases [12]. However, small octanol droplets remain suspended in the aqueous phase, and these small droplets are difficult to remove from the aqueous phase. In particular, for hydrophobic chemicals this will lead to an overestimation of the aqueous concentrations and an underestimation of the true K OW , as well as a large variation in experimental K OW values [13].For We now have 30 to 40 years' experience in applying K OW in research in environmental chemistry and toxicology. The QSAR models based on K OW now appear to be very useful for exposure, hazard, and risk assessment. The advantages of K OW are that experimental data are available for many chemicals and estimates may be obtained from software that is based on the molecular structure of the compound, including EPISUITE [18] and SPARC [19]. Other experimental approaches for predicting K OW are based on comparisons of K OW with retention indices on a C18 high-performance liquid chromatographic column [20].However, octanol does not predict very well the interactions of polar compounds with, for example, a cell membrane, a soil particle, or a humic acid molecule. As ...
This paper presents data on the distribution of seven pesticides in an agricultural catchment which is located within the Agricultural Development and Advisory Service farm at Rosemaund, 11 km north‐east of Hereford, UK. Data for aldicarb, atrazine, carbofuran, dimethoate, MCPA and isoproturon, are available for both the soil and surface waters (drain and stream water), with simazine data available only for the stream. Measurements were taken before and after pesticide application, which was made following normal agricultural practice. Soil residue data showed the degradation rates of the pesticides to be within the range of literature values. Pesticide levels in the stream and drains during runoff events following rainfall ranged from below detection limits (typically 0.02‐0.1 μg/1), to 264 μg/1 (for carbofuran). Over 90% of the events had detectable maximum concentrations. The percentage of pesticide applied, which was removed during individual rainfall events, was calculated. The maximum value estimated was 1.1%, again for carbofuran. Most of the events gave values several orders of magnitude below this value. The data have been used to try to validate a range of models which could be used for screening new pesticides or for informing decisions on the use of existing pesticides. The results of the validations are summarized.
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