Determining High-Quality Critical Body Residues for Multiple Species and Chemicals by Applying Improved Experimental Design and Data Interpretation Concepts

Abstract

Ecotoxicological effect data are generally expressed as effective concentrations in the external exposure medium and do thus not account for differences in chemical uptake, bioavailability, and metabolism, which can introduce substantial data variation. The Critical Body Residue (CBR) concept provides clear advantages, because it links effects directly to the internal exposure. Using CBRs instead of external concentrations should therefore reduce variability. For compounds that act via narcosis even a constant CBR has been proposed. Despite the expected uniformity, CBR values for these compounds still show large variability, possibly due to biased and inconsistent experimental testing. In the present study we tested whether variation in CBR data can be substantially reduced when using an improved experimental design and avoiding confounding factors. The aim was to develop and apply a well-defined test protocol for accurately and precisely measuring CBR data, involving improved (passive) dosing, sampling, and processing of organisms. The chemicals 1,2,4-trichlorobenzene, 1,2,3,4-tetrachlorobenzene, 2,3,4-trichloroaniline, 2,3,5,6-tetrachloroaniline, 4-chloro-3-methylphenol, pentylbenzene, pyrene, and bromophos-methyl were tested on Lumbriculus variegatus (California blackworm), Hyalella azteca (scud), and Poecilia reticulata (guppy), which yielded a high-quality database of 348 individual CBR values. Medians of CBR values ranged from 2.1 to 16.1 mmol/kg wet weight (ww) within all combinations of chemicals and species, except for the insecticide bromophos-methyl, for which the median was 1.3 mmol/kg ww. The new database thus covers about one log unit, which is considerably less than in existing databases. Medians differed maximally by a factor of 8.4 between the 7 chemicals but within one species, and by a factor of 2.6 between the three species but for individual chemicals. Accounting for the chemicals' internal distribution to different partitioning domains and relating effects to estimated concentrations in the target compartment (i.e., membrane lipids) was expected to but did not decrease the overall variability, likely because the surrogate partition coefficients for membrane lipid, storage lipid, protein, and carbohydrate that were used as input parameters did not sufficiently represent the actual partitioning processes. The results of this study demonstrate that a well-designed test setup can produce CBR data that are highly uniform beyond chemical and biological diversity.

A high throughput passive dosing format for the Fish Embryo Acute Toxicity test

“…CBRs are expected to be similar (in the range of 2-8 mmol/kg) among baseline toxicants and small aquatic organisms due to similar mode of action (Van Wezel and Opperhuizen, 1995). Recently, van der Heijden et al (2015) showed that CBR values for seven narcotics tested in three species ranged from 2.1 to 16.1 mmol/kg fresh wt. McCarty et al (2013) reviewed a large set of CBR values and reported a mean CBR of 1.80 mmol/kg fresh wt for 29 narcotics in algae, invertebrates and fish.…”

The chemical exposure toxicity space (CETS) model: Displaying exposure time, aqueous and organic concentration, activity, and onset of toxicity

“…The estimated solubilities in octanol ( S O ) range from 1900 mol m −3 to 2800 mol m −3 for the first 5 chemicals, but a much larger value of 91,700 mol m −3 apparently applies to 4‐Cl‐3‐MP because of the high solubility in water. van der Heijden et al give a lower value of S W by a factor of 2, which still gives a very high value of S O . This high solubility in water is reflected in a very low ILA.…”

“… a Values for log K OW and S W were taken from Mackay et al if available; otherwise EPISuite was used. Values for lipid content ( L ) and CBR are from van der Heijden et al . Values for k 1 , k 2 , ILC, and ILA were calculated for each guppy trial reported by van der Heijden et al , and then an average value was calculated for each chemical (including low, medium, and high concentrations) and reported in this table.…”

“…Linear chemical exposure toxicity space (CETS) concentration plot for the guppy and 1,2,4‐trichlorobenzene tested by van der Heijden et al . The upper red line demarcates the solubility, and the 3 green dashed horizontal lines represent the 3 exposure concentrations.…”

“…Log chemical exposure toxicity space (CETS) concentration plots for the guppy and all chemicals tested by van der Heijden et al . C w = dissolved concentration in the water.…”