Physiological and behavioural responses of Ruditapes decussatus to roundup and reldan

Abstract

The clam Ruditapes decussatus was used as a bioindicator for pollution to determine the toxicity of a herbicide (48% glyphosate, ‘roundup') and an insecticide (50% chlorpyrifosmethyl, ‘reldan'). After estimating LC₅₀ (µl L-1) and LT50 (days) of both organophosphrous pesticides over 60 days, the impact of ½ LC50 of roundup (1.1µl L_-1) and reldan (0.6 µl L_-1) was measured. After two months of treatment, reldan reduced valve activity more than roundup; the rest period increased with increasing time of exposure. There was direct relationship between valve movement and metabolic heat output of respiration and excretion. The decrease in respiration rate was associated with a decrease in ammonia excretion. Thus valve-movement responses of R. decussatus to ½ LC₅₀ of the two pesticides are type-dependent. Both pesticides reduced physiological condition, but reldan is more potent than roundup and its effect is time-dependent. Respiration and excretion rates were components of the energy expenditure that accounted for the decline in metabolism and excretion with increasing the time of exposure to pesticides. This study highlights the potential use of behavioural and physiological response of a sentinel organism for monitoring the pesticides in the marine environment.

KEY WORDS: LC₅₀, glyphosate, chlorpyrifos-methyl, valve movement, oxygen consumption, ammonia excretion, energy lost.

Egyptian Journal of Botany Vol.5 2003: 108-119