Field Comparison of Laboratory-Derived Acute and Chronic Toxicity Data
Authors: Adams WJ , Kimerle RA , Heidolph BB , Michael PR 
Published: March 2009

Standardized laboratory aquatic toxicity tests have been widely accepted as an appropriate means of obtaining the necessary toxicological data needed for conducting aquatic safety assessments of chemicals and for establishing water quality criteria. The need to confirm how well such data predict the toxicity of a chemical in natural environments has long been recognized. To provide insights into the relationship between laboratory and field data, parallel toxicity tests were conducted.

Accepted laboratory methodologies were used for Daphnia magna acute and chronic toxicity tests and for fathead minnow acute toxicity tests and partial life-cycle studies in both the laboratory and the field. The test material was a commercial phosphate ester product containing tert-butylphenyldiphenyl phosphate, triphenyl phosphate, and di-tert-butylphenylphenyl phosphate. For the field study, pond environments were simulated using twelve 3-m diameter tanks. Six ponds contained water and 10 cm of sediment (sediment ponds), and six ponds contained only water (clean ponds). Five concentrations and a control were tested for each series of ponds. Exposure concentrations were maintained by frequent measurements of the test concentrations and spiking of the ponds. The duration of the field test was two months.

The study demonstrates a good relationship between laboratory and field toxicity values for both the acute and chronic data. The laboratory 48-h EC50 value for Daphnia magna was 343 µg/L, compared with a mean of 202 µg/L in the clean ponds and 289 µg/L in the sediment ponds. In similar tests with fathead minnows, the laboratory 96-h LC50 was 3400 µg/L and the field LC50 values were greater than 647 µg/L, the highest field exposure concentration during the 96-h period. The chronic maximum acceptable toxicant concentration (MATC) for Daphnia magna in a laboratory flow-through test was &gt; 40 &lt; 100 µg/L. Similar results (&gt; 40 &lt; 93 µg/L) were observed in a daphnid chronic renewal test using “clean” pond water as the dilution water. Clean and sediment pond chronic MATC values for caged daphnids were &gt; 60 &lt; 136 and &gt; 60 &lt; 226 µg/L, re-specitively. Daphnid population estimates for the clean and sediment ponds demonstrated a strong dose-response relationship and were similar to the results of the cage chronic studies. The estimated no-effect/effect concentrations for fathead minnows in the clean and sediment ponds were &gt; 381 &lt; 545 µg/L and &gt; 453 &lt; 826 µg/L, respectively, as compared with laboratory values of &gt; 140 &lt; 250 µg/L.

Measurements of total (uncentrifuged) and nonbound or soluble (centrifuged) phosphate esters were made throughout the field study exposure period. Approximately 50% of the total material was present in soluble form. Theoretical calculations are presented comparing the water solubilities and soil partition coefficients of several chemicals with predicted soluble (nonbound) concentrations in natural environments. The calculations suggest that most nonpolar chemicals studied to date will exist in aquatic environments in a soluble form and not be absorbed to suspended particulates. This can be predicted on the basis of a chemical's water solubility or soil partition coefficient.

These studies provide evidence that current laboratory acute and chronic tests with Daphnia magna and fathead minnows provide realistic estimates of a chemical's toxicity to the same species in simulated natural environments and should provide reasonable estimates of toxic effects on populations in natural aquatic ecosystems. They also suggest that the ability to predict the toxicity of a chemical in the environment lies in an under-standing of the impact of the environment on the exposure concentration.