Biomarkers and energy reserves in the isopod Porcellionides pruinosus: the effects of long-term exposure to dimethoate.

Terrestrial isopods from the species Porcellionides pruinosus were exposed to the recommended field dose application (0.4 mg/kg soil) and a sublethal concentration (10mg/kg soil) of dimethoate at two temperatures that can be generally found in several countries (20°C and 25°C) and are commonly used as reference temperatures. The organisms were exposed for 28 days and sampled at the following time points: 24h, 48 h, 96 h, 7 days, 14 days, 21 days, 28 days; organisms were then changed to clean soil for a recovery period of 14 days during which organisms were sampled on day 35 and 42. For each sampling time, the enzyme activities of acetylcholinesterase (AChE), glutathione-S-transferases (GST), catalase (CAT), lactate dehydrogenase (LDH) were determined as well as the following: total lipid, carbohydrate and protein content; energy available (Ea); energy consumption (Ec); cellular energy allocation (CEA) and lipid peroxidation rate (LPO). The integrated biomarker response (IBR) was calculated for each sampling time and for each of the above parameters. Mortality was also recorded during the study. The results obtained showed that dimethoate causes toxicity by several mechanisms. This study found evidence for the inhibition of the acetylcholinesterase enzyme, which has been previously reported, and also evidence of oxidative stress, which altered the levels of GST, CAT or LPO. In addition, the study showed that the two concentrations used of dimethoate caused the activation of different general detoxification mechanisms, and also that the same concentration at different temperatures induced different toxicity responses.