An equation describing the time course and variability in uptake and toxicity of narcotic chemicals to fish

Abstract

An equation is proposed to express the time course of uptake of organic chemicals by fish. The chemicals' octanol/water partition coefficients are used to describe equilibrium partitioning, whereas the clearance rate constant, estimated as a function of water‐ and organic‐phase series resistances to transport, is used to describe the time course of uptake. The probability of the concentration of chemical in the fish causing a defined toxic end point is expressed by using a modified Weibull distribution function that contains an adjustable parameter describing variability in organism response. The effect of metabolism can be included if desired. The combined uptake and probability equations are tested by using mortality data for fathead minnows exposed to 18 narcotic chemicals. A single set of parameters is obtained to fit the entire data set. The equation highlights the importance of considering the kinetics of toxicant accumulation when interpreting toxicity results, especially for hydrophobic chemicals, and reinforces the fact that a common organism residue level (in either molar volume or molarity) is associated with 50% mortality in acute bioassays with narcotic organic chemicals. Assorted features of the equations and their applicability to toxicants with specific modes of action are discussed.

Environmental Risk Assessment of Agrochemicals — A Critical Appraisal of Current Approaches

“…It has long been suggested that toxicity tests should include information not only on doses or concentrations but also on exposure time [34][35][36], with time-to-effect bioassays being a practical way to achieve this [37]. Toxicokinetics are necessary to interpret the toxicity of a compound with time of exposure [38,39], because they can relate time-dependent toxicity to target organ concentrations [40]. For some compounds, toxic effects may depend almost exclusively on the total dose [41], whereby the product of dose, or concentration, and exposure time produces the same biological effect (Haber's rule).…”

Radionuclides, Metals, and Hydrocarbons in Oil and Gas Operational Discharges and Environmental Samples Associated with Offshore Production Facilities on the Texas/Louisiana Continental Shelf with an Environmental Assessment of Metals and Hydrocarbons.

“…Considerable progress has been made in recent years in developing quantitative structure activity relationships (QSARs) that relate physical/chemical properties of non-specific toxicants, particularly nonpolar organic chemicals, to biological end points, such as acute or chronic toxicity and bioaccumulation (McCarty, 1986;Abernethy et al, 1988;Warne et al, 1991;Connell and Markwell, 1992;Mackay et al, 1992a;Van Leeuwen et al, 1992;Sijm et al, 1993). showed, that for nonpolar organic chemicals that are non-specific toxicants (act primarily by physical accumulation in membrane lipids, causing generalized narcotic effects), the critical body residue (CBR) of the chemical in the whole tissues of the animal is approximately 4.4 mmol/kg wet weight (95% C.I.…”

A model describing the time course and variability in toxicity of hydrophobic chemicals to aquatic organisms

“…Until now, no simple and quantitative explanation for this phenomenon could be given (Geyer et aL, 1994). There are several possible reasons (Geyer et al, 1994;Mackay et al, 1992) why the toxicity may be misunderstood. First, HOCs may appear to have a low toxicity because the test organism takes them up slowly.…”

“…In addition, HOCs may appear to have different toxicities under different growth conditions because growth has a considerable effect on the bioconcentration of HOCs in or-ganisms, in particular for HOCs with high Kow values (Gobas, 1993). Finally, some HOCs may be readily metabolized by the test organism, thus decreasing the concentration of the parent HOC in the organism, and hence either reducing the apparent toxicity or forming an active metabolite that educes the primary toxic response (Mackay et al, 1992). Mackay et al (1992) proposed a set of equations to provide an approximate description of the characteristics of HOC toxicity to aquatic organisms from experimental data for mortality-HOC exposure concentration-exposure time.…”

“…Finally, some HOCs may be readily metabolized by the test organism, thus decreasing the concentration of the parent HOC in the organism, and hence either reducing the apparent toxicity or forming an active metabolite that educes the primary toxic response (Mackay et al, 1992). Mackay et al (1992) proposed a set of equations to provide an approximate description of the characteristics of HOC toxicity to aquatic organisms from experimental data for mortality-HOC exposure concentration-exposure time. In these equations, the uptake rate constant, k l, and the elimination rate constant, k2, can be obtained from experimental data.…”