Comparative sensitivity of the cnidarian Exaiptasia pallida and a standard toxicity test suite: testing whole effluents intended for ocean disposal.

The sea anemone Exaiptasia pallida (formally Aiptasia pulchella) has been identified as a valuable test species for tropical marine ecotoxicology. Here, the sensitivities of newly developed endpoints for E. pallida to two unidentified whole effluents were compared to a standard suite of temperate toxicity test species and endpoints that are commonly used in toxicological risk assessments for tropical marine environments. For whole effluent 1 (WE1), a 96-h lethal concentration 50 % (LC50) of 40 (95 % confidence intervals, 30-54) % v/v and a 12-day LC50 of 12 (9-15) % v/v were estimated for E. pallida, exhibiting a significantly higher sensitivity than standard sub-lethal endpoints in Allorchestes compressa (96-h effective concentration 50 % (EC50) of >100 % v/v for immobilisation) and Hormosira banksii (72-h EC50 of >100 % v/v for germination), and a similar sensitivity to Mytilus edulis galloprovincialis larval development with a 48-h LC50 of 29 (28-30) % v/v. Sub-lethal effects of whole effluent 2 (WE2) on E. pallida pedal lacerate development resulted in an 8-day EC50 of 7 (3-11) % v/v, demonstrating comparable sensitivity of this endpoint to standardised sub-lethal endpoints in H. banksii (72-h EC50 of 11 (10-11) % v/v for germination), M. edulis galloprovincialis (48-h EC50 for larval development of 12 (9-14) % v/v) and Heliocidaris tuberculata (1-h EC50 of 13 (12-14) % v/v for fertilisation; 72-h EC50 of 26 (25-27) % v/v for larval development) and a significantly higher sensitivity than A. compressa immobilisation (96-h EC50 of >100 % v/v). The sensitivity of E. pallida compared to a standard test species suite highlights the value in standardising the newly developed toxicity test methods for inclusion in routine toxicological risk assessment of complex whole effluents. Importantly, this species provides an additional taxonomic group to the test species that are currently available for tropical marine ecotoxicology and, being a cnidarian, may represent important tropical marine environments including coral reefs.

Joint acute toxicity of diazinon and ammonia to Ceriodaphnia dubia.

Diazinon is an organophosphorous pesticide widely found in municipal effluents as well as in agricultural and urban storm-water discharges. Ammonia is frequently also present in such effluents as a consequence of bacterial degradation of organic material. Because these two contaminants may occur concurrently, their relationship with respect to joint toxicity is of interest, particularly in regard to interpreting the results of effluent tests and subsequent toxicity identification evaluations (TIEs). In this particular case, we obtained an effluent sample that exhibited toxicity to Ceriodaphnia dubia. Toxicity identification evaluations manipulations suggested that ammonia (40 mg\L as total NH3) and diazinon (0.75 microgram/L) both contributed to toxicity. As part of the Phase 3 confirmation studies, an independent investigation was conducted to evaluate the interactions between these two toxicants using static tests that incorporated a 48-h exposure period. Chemical concentrations were verified analytically. Mortalities were measured at 24-h intervals and joint toxicity calculated on the basis of toxic units (TUs) for each toxicant. The 48-h LC50 values (lethal concentrations for 50% of the population) for the individual chemicals averaged 0.36 microgram/L and 1.11 mg/L for diazinon and un-ionized ammonia, respectively. Under the assumption of strict additivity, the sum of TUs contributed by each toxicant at the LC50 of the mixture should total unity. The TUs associated with the mixtures in laboratory water averaged 1.37 and 1.47, respectively, for 24- and 48-h exposure intervals. These results were similar to those obtained with the actual effluent sample and suggest that diazinon and ammonia exhibit less than additive toxicity when present together.