Lowest-observable effect concentrations LOECs

TCDD concentrations in eggs of seven species after exposure as fertilized eggs to nominal concentrations of 9-285 ng 2,3,7,8-TCDD/L for up to 540 h. Lowest observed effect concentration (LOEC) in ng/kg FW associated with adverse effects on su rvival or growth 32 days post exposure vs. no observed effect concentration (NOEC) in ng/kg FW Lake herring, Coregonus artedi 270 vs. 175 Fathead minnow, Pimephales promelas ... 

TEC, threshold effect concentration, calculated as the geometric mean of the no-observable effect concentration (NOEC) and the lowest-observable effect concentration (LOEC) BA Battery Approach PW porewater WS whole sediments. 

Within the USEPA s EPI Suite, descriptions of basic physical-chemical properties for 2,4-dichloroaniline (DCA CAS No. 554007), pentachlorophenol (PCP CAS No. 87865), nonylphenol (NP CAS No. 104405), and linear alkylbenzenesulfonate (C12 LAS CAS No. 25155300) were obtained using the EPI Suite (Table 3.1), whereas acute and chronic toxicity estimates for the median effective and chronic effect concentrations (the geometric mean between chronic lowest-observed-effect concentration [LOEC] and no-observed-effect concentration [NOEC]) and for fish, daphnids, and algae for each substance were estimated from ECOSAR (Table 3.2). These compounds were chosen based on their widespread use. 

In addition, the size of the effect at the Lowest Observed Effect Concentration (LOEC) might vary considerably from test to test. 

Class II slight acute hazard = the lowest observed effective concentration (LOEC) is reached in at least one test but the effect level is below 50%. 

The potential for phytotoxicity from explosives is discussed at length elsewhere in this volume (see Chapter 3). Few studies of the phytotoxicity of these chemicals have been undertaken, and most of these, which are reviewed in Rocheleau et al. [13], were tests of TNT. Concentrations of TNT that reduce shoot or root biomass in crop test plants in the laboratory range from about 0.1 mg kg-1 to >1600 mg kg 1 dry soil [14-17], Phytotoxicity tests with amended soils produced lowest observed effect concentration (LOEC) values for TNT ranging from 0.1 to 64 mg kg 1 depending on plant species and exposure type used [15] (see Chapter 3). Plant growth was not affected by HMX at concentrations up to approximately 1900 mg kg1 dry forest soil [16], and additional studies suggest that nitroheterocyclic compounds are not as toxic... 

During this step of risk assessment, a chemical s dose-dependent toxicological properties are of interest. A substance is studied at different concentrations (doses) in biological assays (e.g., oral dosing over 90 days in rodents to assess sub-chronic toxicity) for determining the lowest observed effect concentration (LOEC). This information can then be used to derive a no observed effect concentration (NOEC), a level that is of interest for human health risk assessment. Effects observed in laboratory animal studies may vary depending on the dose, life stage, duration and route of exposure, and sex and strain of the test animal. 

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