Organophosphorus insecticides have been the most applied group of
insecticides for the last two decades. Their main toxic effects are related
to irreversible inactivation of acetylcholinesterase (AChE). Actually, they
covalently bind to serine OH group in the enzyme active site forming
phosphorylated enzyme that cannot hydrolyze acetylcholine. Organophosphorus
insecticides in the environment undergo the natural degradation pathway
including mainly homogeneous and heterogeneous hydrolysis (especially at high
pH) generating non-inhibiting products. Additionally, thio organophosphates
are easily oxidized by naturally present oxidants and UV light, forming more
toxic and stable oxons. Thus, oxidative degradation procedures, generally
referred as advanced oxidation processes (AOP), have been applied for their
efficient removal from contaminated waters. The most applied bioassays to
monitor the organophosphate toxicity i.e. the detoxification degree during
AOP are Vibrio fischeri and AChE bioassays. Vibrio fischeri toxicity test
exploits bioluminescence as the measure of luciferase activity of this marine
bacterium, whereas AChE bioassay is based on AChE activity inhibition. Both
bioanalytical techniques are rapid (several minutes), simple, sensitive and
reproducible. Vibrio fischeri test seems to be a versatile indicator of toxic
compounds generated in AOP for organophosphorus insecticides degradation.
However, detection of neurotoxic AChE inhibitors, which can be formed in AOP
of some organophosphates, requires AChE bioassays. Therefore, AChE toxicity
test is more appropriate for monitoring the degradation processes of thio
organophosphates, because more toxic oxo organophosphates might be formed and
overlooked by Vibrio fischeri bioluminescence inhibition. In addition, during
organophosphates removal by AOP, compounds with strong genotoxic potential
may be formed, which cannot be detected by standard toxicity tests. For this
reason, determination of incidence of micronuclei and cell proliferation
index in cultivated human lymphocytes and fibroblasts is suitable for
evaluation of organophosphorus insecticides and their break down products
inducing cytogenetic damage.
Organophosphorus insecticides: Toxic effects and bioanalytical tests for evaluating toxicity during degradation processes
