PARENT SESSION

PT09 Biotic Ligand Model
Exhibit Hall
8:00 AM - Tuesday, 11 November 2003

(PT161) Silver toxicity in the euryhaline copepod Acartia tonsa (Copepoda, Calanoidea).

Pedroso, M¹, Bianchini, A¹, ¹ Departamento de Ciências Fisiológicas - FURG, Rio Grande, RS, Brazil

ABSTRACT- According to the BLM approach developed for fresh water, different complexing agents such as NOM and the anions Cl^-, OH^-, HCO₃^-, and CO₃^2- can modify silver toxicity. Competition at biological membranes by cations such as Na⁺, Ca²⁺, and Mg²⁺ can also alter silver toxicity. Our objective was to determine silver toxicity to the euryhaline copepod Acartia tonsa in a wide range of salinities, in either the absence or the presence of food in the water. Male and female adult copepods were acclimated to three different salinities (5, 15, and 30), for at least one week. Copepods were fed a mixture of diatoms. Groups of 10 copepods were exposed to different concentrations of silver (AgNO₃), for 48 h. Silver toxicity was determined in the absence or in the presence of food (10⁴ cells/mL) using a standard static-renewal system. Tests were run in duplicate. Based on nominal concentrations and in the absence of food, the 48-h LC50 values (g/L) were 26.0, 65.8, and 59.6, for salinities 5, 15 and 30, respectively. In the presence of food, they were 48.3, 76.3, and 43.7. Silver toxicity is dependent on salinity in both the presence and the absence of food. In the absence of food, silver toxicity is higher in diluted seawater (salinity 5). Silver toxicity is modified by the presence of food in the water. The influence of food on silver toxicity is dependent on water salinity, being significant in diluted seawater (salinity 5) and negligible in salinities 15 and 30. Overall, our results are in accord with the BLM approach originally developed for freshwater systems.

Key words: euryhaline copepod, silver, acute toxicity, varied salinity