Comparative study of toxic lead effect on gill and haemoglobin of tilapia fish.

This study was designed to determine the 72-h LC50 of lead for tilapia fish (Oreochromis hornorum), as well as the effect of exposure to sublethal lead concentrations (15, 23, 31, 39 and 47% of the LC50) on gill tissue lysosomal membranes of the fish and thaemoglobin concentration in blood. The LC50 value was found to be 202 mg Pb2+ l-1. Exposure to sublethal lead concentrations for 72 h showed significant increases in the lability of gill lysosomal membranes, measured by the release of acid phosphatase. Changes in membrane lability and in haemoglobin concentration were dependent on the amount of lead used during the exposure. We considered that the membrane lability is an adequate parameter to assay for monitoring lead contamination in water, because it is more sensitive than the haemoglobin concentration in blood.

Relationship between toxicokinetics of carbaryl and effect on acetylcholinesterase activity in Pomacea patula snail.

The 96-h LC(50) value of carbaryl was 14.6 microg/mL for the snail Pomacea patula. Organisms were exposed for 72 h to a low sublethal concentration (0.1 of LC(50)) using a semistatic contamination system; bioconcentration and elimination experiments were performed evaluating simultaneously acetylcholinesterase (ACHase) activity. The inhibition of the digestive gland ACHase reached 76% when the carbaryl concentration in tissue was 3.2 microg/g. The increased enzyme inhibition was observed concomitantly with the bioconcentration of carbaryl until 7 h. ACHase inhibition was linearly dependent on the uptake and bioconcentration of carbaryl (r(2)=0.87). The transfer of snails to carbaryl-free water after 72 h of exposure was followed by rapid monophasic elimination with a half-life of 1.0 h. However, ACHase activity levels never returned to control values. These results revealed that the bioconcentration might play a critical role in contributing to the toxicity of carbaryl.