Quantifying the sorption of organic chemicals on sediments

The use of a reference compound to quantify the sorption of nonpolar organic chemicals is proposed. This is because organic carbon normalized sorption coefficients (K_OC) do appear to be dependent on the type of sediment, and are thus not generally applicable to characterize the sorption properties of chemicals. Therefore, in this paper the hypothesis that nonpolar chemicals sorb in a constant ratio, independent of the sediment, has been investigated. Evidence for this hypothesis is shown with data from the literature. This enables one to compare sorption properties of nonpolar compounds on different sediments, if the differences between the sediments are normalized with a reference chemical rather than with the organic carbon content. Sediments with an organic carbon content of less than 0.1% seem to be unsuitable, because the compounds do not sorb mainly on the organic carbon, but also on other parts of the sediment. Sorption coefficients of compounds with aqueous solubilities in the μg per liter range or octan-1-ol water partition coefficients of more than 10⁵ are strongly influenced by the experimental techniques used. For these compounds the sorption coefficients measured by different techniques are less comparable. To enable comparison of sorption coefficients of hydrophobic chemicals, the use of a chlorobenzene as a reference compound in sorption experiments is suggested.     

Multi-criteria analysis and risk assessment

ELECTRE or Concordance Analysis is a French system of multicriteria analysis which is used in economics.The application of ELECTRE for hazard evaluation and risk assessment of chemical substances is suggested, and a first attempt in adapting it for this purpose is presented.     

Biotransformation rates of xenobiotic compounds in relation to enzymes activities: A critical review

Many biotransformation reactions and many activities of enzymes involved in the biotransformation of xenobiotics in fish have been described. Therefore, the prediction of biotransformation of (other) xenobiotics through literature data seems to be possible. However, very few data allow correlation of in vitro enzyme activities with in vivo biotransformation rates. This is mainly due to a lack of quantitative data. Suggestions are made for future research, which may help to relate enzyme activities and biotransformation in fish.     

Relationships between octan‐1‐ol/water partition coefficients,aqueous activity coefficients and reversed phase HPLC capacity factors of alkylbenzenes,chlorobenzenes, chloronaphthalenes and chlorobiphenyls

Linear relationships between logarithms of octan‐1‐ol/water partition coefficients (K_d,oct), aqueous activity coefficients (y_aq) and extrapolated RP HPLC capacity factors (k‘_w) are found for four types of aromatic hydrocarbons (alkylbenzenes and poly‐chlorinated benzenes, ‐naphthalenes and ‐biphenyls).

Both log K,_d,oct and logk‘_w increase with the increasing number of chlorine or methyl‐ene substituents. These increases of log K,_d,oct and log k‘_w are proportional and almost independent of the parent compound. In addition, these increases are linear to increases of logy_aq. The slopes of logk‘_w‐logy_aq and log K,_d,oct‐logv_aq relationships deviate significantly from 1.0. This suggests that the activity coefficients of the test compounds in both octan‐1‐ol and in the stationary phase of the RP column increase after substitution of aromatic compounds with methylene or chlorine.     

Uptake and elimination kinetics of triphenyltin hydroxide by two fish species

The uptake from water and the elimination of carbon‐14 radiolabelled triphenyltin hydroxide ([¹⁴C]TPTH) was studied in two fish species: guppy (Poecilia reticulata) and rainbow trout larvae (Salmo gairdneri). During all the experiments no steady state in fish was found. TPTH was rapidly taken up, while elimination was very slow. Uptake and elimination rate constants (k ₁ and k ₂, respectively), and a bioconcentration factor were estimated, assuming first order kinetics.

During eight days of exposure of guppy to TPTH an uptake rate constant k ₁ of 70±7L/kg.d and an elimination rate constant k ₂ of 0.005 ±0.029d ^‐1 was found. This resulted in a biconcentration factor of at least 2.1 × 10³L/kg (wet weight). Comparable results were obtained during a 30 days exposure experiment with guppy: k ₁ was 41±2L/kg.d, k ₂ 0.014 + 0.002d^‐1, and the bioconcentration factor was estimated to be 2.9 × 10³ L/kg (wet weight).

Four days exposure of rainbow trout larvae resulted in a it, of 22+ 2 L/kg.d, and a k ₂ of 0.031 ±0.007d^‐1. Using these k, and k ₂ values it was estimated that the biconcentration factor exceeds 650 L/kg (wet weight).     

Relationship between bioconcentration in fish and steric factors of hydrophobic chemicals

Most polychlorinated naphthalones (PCN) accumulate rapidly according to their hydrophobicity. The uptake and ellmination rate constants are comparable to those of chlorinated benzenes and biphenyls.For most PCN-congeners the resulting bioaccumulation factors show an increase with increasing hydrophobicity. For higher K_d,oct-values (>10⁵) however, no further increase of K_c is observed (K_c. max. = 3.5.10⁴).For the two hepta- and the octachloronaphthalenes no detectable concentrations are found in the fishes, although no restricted blo-availability could be expected. Based on these observations and on data obtained from the literature. a loss of membrane permeation is suggested for hydrophobic molecules with widths over 9.5 Å.In addition a membrane permeation model, as part of the accumulation process of hydrophobic chemicals. Is proposed, which is based on diffusion and partition processes.     

Bioconcentration kinetics of 2,4,5- tri- and 3,3′,4,4′-tetrachlorobiphenyl and 2,4,5- tri- and 3,3′,4,4′-tetrachlorodiphenylether in fish

The rates of uptake and elimination of 2,4,5 tri- and 3,3′,4,4′-tetrachlorodiphenylether in fish after aqueous exposure are comparable to those of similarly substituted chlorobiphenyls. Mass balance data suggest that 2,4,5- trichlorobiphenyl and 2,4,5- trichlorodiphenylether are metabolized with rates approximately twice as high as the rates of elimination of the parent compounds.The bioconcentration factors of the 3,3′,4,4′-tetrachloro- biphenyl and 3,3′,4,4′- tetrachlorodiphenyl ether are only determined by the hydrophobic nature of these chemicals and are not influenced by metabolism. Congener specific uptake and elimination processes as have been reported for chlorinated dibenzo-p-dioxins and dibenzofurans does not seem to be important for chlorinated biphenyls and diphenylethers.     

Absorption and retention of polydimethylsiloxanes (silicones) in fish: Preliminary experiments†

Hydrophobicity and bioaccumulation potential of linear and cyclic polydimethylsiloxane (PDMS) oligomers were estimated by reversed‐phase liquid chromatography and feeding experiments with guppies (Poecilia reticulata). PDMS concentrations in fish were determined by capillary column gas chromatography and gas chromatography‐mass spectrometry. In contrast to polychlorinated biphenyls (PCBs), only very small amounts of PDMS were retained by the fish after six weeks feeding.     

Influence of contaminated particles on the bioaccumulation of hydrophobic organic micropollutants in fish

The influence of contaminated particles on the bioconcentration of hydrophobic chemicals by fish is dependent on the hydrophobicity of the chemicals. This has been shown for polychlorinated benzenes and biphenyls (ranging over three orders of magnitude in octan-1-ol/water partition coefficient) which are sorbed on very low organic carbon content particles. For chemicals with low to moderate hydrophobicity, the amount of the chemical which is sorbed, relative to the amount which is dissolved, determines the influence that contaminated particles have on the uptake of the chemicals by fish. In this present experiment, for lower chlorinated benzenes and biphenyls, the amount dissolved in water are high compared with the amounts which are present in the sorbed state, and the influence of contaminated particles on their uptake by fish is negligible. For more hydrophobic chemicals, which have lower aqueous solubilities, such as penta and hexachlorobenzene, and tri and tetrachlorobiphenyls, contaminated particles can have a much greater influence on the uptake by fish. If the number of contaminated particles is sufficiently high, the low aqueous solubilities, in combination with relatively high rates of desorption or dissolution, enable the particles to act as a source of the hydrophobic chemicals. For extremely hydrophobic chemicals, the rates of dissolution or desorption determine the rates of uptake of the chemical by the fish. Hence, during relatively short periods of exposure, there is no influence of contaminated particles on the bioaccumulation.