There is an increasing body of evidence that the bioaccumulation of sediment-associated hydrophobic organic compounds (HOCs) is strongly influenced by sequestration. At present, it is not known how equilibrium partitioning theory (EqP), the most commonly employed approach for describing sediment bioaccumulation can be applied to sediments with sequestered contaminants. In this paper, we present freely dissolved pore-water concentrations of HOCs. These data were employed to interpret sediment bioaccumulation and sequestration data in order to arrive at a process based evaluation of EqP. The data analysis suggests that sediment bioaccumulation of compounds up to log K(ow) 7.5 in Tubificidae can be described as bioconcentration from pore-water. In addition, the pore-water concentrations of HOCs (4.5 < log K(ow) < 7.5) are established by equilibrium partitioning between the rapidly desorbing HOCs fraction in the sediment and the pore-water. Taken together, these findings indicate that EqP is a conceptually correct representation of sediment bioaccumulation, provided that sequestration is accounted for. This implies that the risk assessment of sediment-associated HOCs can be significantly simplified: With a method at hand for measuring freely dissolved pore-water concentrations of HOCs, it appears that HOCs' body residues in sediment dwelling organisms can be estimated on the basis of concentrations in pore-water and bioconcentration factors.

The OECD test guideline 203 for determination of fish acute toxicity requires substantial numbers of fish and uses death as an apical end point. One potential alternative are fish cell lines; however, several studies indicated that these appear up to several orders of magnitude less sensitive than fish. We developed a fish gill cell line-based (RTgill-W1) assay, using several measures to improve sensitivity. The optimized assay was applied to determine the toxicity of 35 organic chemicals, having a wide range of toxicity to fish, mode of action and physicochemical properties. We found a very good agreement between in vivo and in vitro effective concentrations. For up to 73% of the tested compounds, the difference between the two approaches was less than 5-fold, covering baseline toxicants but as well compounds with presumed specific modes of action, including reactivity, inhibition of acetylcholine esterase or uncoupling of oxidative phosphorylation. Accounting for measured chemical concentrations eliminated two outliers, the hydrophobic 4-decylaniline and the volatile 2,3-dimethyl-1,3-butadiene, with an outlier being operationally defined as a substance showing a more than 10-fold difference between in vivo/in vitro effect concentrations. Few outliers remained. The most striking were allyl alcohol (2700-fold), which likely needs to be metabolically activated, and permethrin (190-fold) and lindane (63-fold), compounds acting, respectively, on sodium and chloride channels in the brain of fish. We discuss further developments of this assay and suggest its use beyond predicting acute toxicity to fish, for example, as part of adverse outcome pathways to replace, reduce, or refine chronic fish tests.

Experimental data are presented on octanol/water partition coefficients for 70 hydrophobic organic chemicals that were determined with a "slow-stirring" method. With this method, log KO, values can be obtained relatively easily, with high reproducibility and low standard deviations. For compounds with log KO, values of less than 4.5, the experimental data agree well with literature data based on the classical shake-flask method. For more hydrophobic compounds, deviations occur because of the formation of octanol emulsions in the shake-flask procedure. In general, there is reasonable agreement with literature data obtained by reversed-phase HPLC or the generator-column method, although substantial deviations do occur for some individual compounds, especially the higher-chlorinated ortho-substituted polychlorinated biphenyl (PCB) congeners. For chlorobenzenes, chloroanilines and PCBs, substituent constants ( T ) are calculated. With these T values, partition coefficients for these compounds can be estimated simply by calculation.

The zebrafish embryo toxicity test has been proposed as an alternative for the acute fish toxicity test, which is required by various regulations for environmental risk assessment of chemicals. We investigated the reliability of the embryo test by probing organic industrial chemicals with a wide range of physicochemical properties, toxicities, and modes of toxic action. Moreover, the relevance of using measured versus nominal (intended) exposure concentrations, inclusion of sublethal endpoints, and different exposure durations for the comparability with reported fish acute toxicity was explored. Our results confirm a very strong correlation of zebrafish embryo to fish acute toxicity. When toxicity values were calculated based on measured exposure concentrations, the slope of the type II regression line was 1 and nearly passed through the origin (1 to 1 correlation). Measured concentrations also explained several apparent outliers. Neither prolonged exposure (up to 120 h) nor consideration of sublethal effects led to a reduced number of outliers. Yet, two types of compounds were less lethal to embryos than to adult fish: a neurotoxic compound acting via sodium channels (permethrin) and a compound requiring metabolic activation (allyl alcohol).

Experimental data are presented on octanol/water partition coefficients for 70 hydrophobic organic chemicals that were determined with a “slow‐stirring” method. With this method, log Kow values can be obtained relatively easily, with high reproducibility and low standard deviations. For compounds with log Kow values of less than 4.5, the experimental data agree well with literature data based on the classical shake‐flask method. For more hydrophobic compounds, deviations occur because of the formation of octanol emulsions in the shake‐flask procedure. In general, there is reasonable agreement with literature data obtained by reversed‐phase HPLC or the generator‐column method, although substantial deviations do occur for some individual compounds, especially the higher‐chlorinated ortho‐substituted polychlorinated biphenyl (PCB) congeners. For chlorobenzenes, chloroanilines and PCBs, substituent constants (π) are calculated. With these π values, partition coefficients for these compounds can be estimated simply by calculation.