Journal of Taiwan Agricultural Research

Author:Ching-hua Kao*, Chia-lin Tzeng and Edward Y. Cheng

Abstract:

    Among several pesticides registered for the protection of rice crop in Taiwan, more than 40 organophosphorus and carbamate insecticides have caused concern due to their residues in harvested rice. Although chemical analysis of residues has been applied to rice, a rapid method to detect harmful levels of pesticide residues will be helpful before residue-contaminated rice is stored, processed or marketed. The residues most commonly detected in rice are those of anticholinergic agents such as, methamidophos, acephate, ethion, pirimiphos-methyl, carbofuran, carbaryl, methomyl, and BPMC. A rapid and highly sensitive acetyicholinesterase test, the rapid bioassay of pesticide residues (RBPR), that has currently been used to detect residues of organophosphate and carbamate insecticides in fruits and vegetables, was modified and tested on three groups of rice samples with known quantities of pesticide residues. Twenty-five samples, classified as group I, had no pesticide residues; 28 samples, classified as group II, contained organophosphorus and carbamate residues under the tolerance level; and 6 samples, classified as group III, contained residues of above-mentioned insecticides above tolerance level. All 59 samples, extracted by whole grain extraction or freshly ground powder extraction, were tested for their anticholinergic activity. The whole grain extraction showed group I samples to have average acetylcholinesterase inhibition of merely 6.7%; group II, 27.6%; while group III, 60.2%. The 95% confidence range of the means of group I, II, and III were statistically separable and ranged from 1.8-11.6%, 20.0-35.3%, and 41.2-79.1%, respectively. The acetylcholinesterase inhibition correlated positively with the chemical analysis of organophosphorus and carbamate residues. In extraction of ground rice, two samples in group III varied considerably resulting in overlapping of 95% confidence ranges of group II and III. The study indicated that the acetyicholinesterase test is sensitive enough to detect the residues of insecticide in rice without interference of plant chemicals in rice, and it is quantitatively correlated to chemical analysis of insecticide residues. Between two extraction methods, the whole grain treatment is preferred over rice powder method. In a hypothetic analysis of 59 samples, with detection threshold set at 60%, 50%, and 40 % acetylcholinesterase inhibition, the correct detection rate for violation were 50.0%, 66.7%, and 88.3%, respectively. The detection of false negatives, decreased to 5.5%, 3.9%, and 2.1%, while unnecessary rejection rate increased from 40%, 50%, and 58%, respectively. The acetylcholinesterase inhibition test can be used effectively in (1) verification of organic rice, (2) comparison of safety of rice from different regions, seasons and year, (3) providing indexes of total toxicity of organophosphorus and carbamate insecticide residues to fit the requirement of FQPA. The reliability, economy, time saving, and user-friendly characteristics of RBPR will facilitate screening of larger number of rice samples within a very short period for gathering basic safety information.

Key words:RBPR, Rice, Organophosphorus insecticides, Carbamate insecticides, Acetylcholinesterase

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