Changes in phosphoadenylate concentrations and adenylate energy charge as an integrated biochemical measure of stress in invertebrates: The effects of cadmium on the freshwater clamCorbicula fluminea

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Abstract
Concentrations of phosphadenylates ATP, ADP and AMP were measured in foot muscle tissue of the Asian clam, Corbicula fluminea Müller, by the luciferin‐luciferase bioluminescence technique. Total adenylate concentration μM · g‐ 1, dry weight and adenylate energy charge [AEC = (ATP+1/2ADP)/(ATP + ADP + AMP] were calculated. The effects of laboratory acclimation, starvation and exposure to 0.005, 0.05, 0.5 and 5.0mgCd · l‐1 were investigated. We observed no significant difference between the AEC of clams collected from the Savannah River Channel below Augusta, Georgia and those collected from Clark Hill reservoir on the Savannah River above Augusta. When C. fluminea, collected from the Savannah River were taken to the laboratory and fed and maintained in aerated water at 21°C, the AEC increased from 0.76±0.06 to 0.95±0.01 (x±95% CI, n = 8). This indicates that C. fluminea in the Savannah River were living under sub‐optimal conditions. Starvation for 10 and 20 days did not significantly decrease the AEC. However, starvation caused the AEC to decrease from 0.80 to 0.37 between 20 and 30 days of starvation. The 96‐hr LC50 for cadmium exposure was 32mgCd · l‐1 at 21°C. In a short‐term study, exposure to 4.8 and 0.6 mg Cd·l‐1 decreased the AEC significantly, relative to controls after 4 and 9 days. In a more extensive study, 50 μg Cd · l‐1 caused a reduction in AEC, but this decrease was not significant (α=0.05). Exposure to both 0.5 and 5.0mg Cd · l‐1 caused significant decreases in AEC. These decreases in AEC were accompanied by significant decreases in ATP and total adenylate concentrations only when clams were exposed to 5 mg · l‐1. The AEC of clams exposed to 5 mg Cd · l‐1 decreased to 0.54 after 9 days of exposure. When the 5 mg · l‐1 Cd exposure was terminated, the AEC continued to decrease to 0.42 at day 16 just before the last of the experimental organisms died. When exposure to 0.05 μg Cd · l‐1 was terminated after 16 days the AEC returned to values which were not significantly different from those of control organisms. Due to its sensitivity to toxicants and metabolic universality, the AEC, while not a panacea for environmental monitoring, may be a useful tool in an integrated program of environmental monitoring.