The lethal body burden (LBE) was determined in guppies (Poecilia reticulata) that died of exposure to four individual organophosphorous pesticides at two different concentrations. For bromophos and fenthion, LBB values of 5.00 and 11.3-mu-mol/g fish, respectively, were observed and these values were independent of the time of death of the fish and of the aqueous concentrations offered. The behavioural toxicity syndromes largely corresponded to effects of chemicals that act by narcosis. At low exposure levels of chlorothion and methidathion much lower LBB values were found (0.41 and 0.0025-mu-mol/g fish, respectively), probably due to a more specific mode of action. However, fish that died within 24 h after exposure to high concentrations of these compounds had LBB values that were 6 to 10 times higher. Thus, lethal body burdens of these chemicals might depend on time of death and exposure concentration. Therefore, it is recommended that LBB experiments should last for several days in order to achieve a sufficient distribution of the chemical in the fish body. It was also observed that the bioconcentration factor of chlorothion at lethal exposure levels was a factor of 10 higher than the bioconcentration at sublethal levels. This dependence on aqueous exposure levels of the administered chemical may be caused by effects on the biotransformation processes.
