Field study on exposure and health effects of an organophosphate pesticide for maintaining registration in the Philippines

To support the continued use and the registration of monocrotophos, a field study was conducted at Calauan, Laguna, The Philippines, to assess exposure and the resulting health risk to 21 spraymen applying monocrotophos to rice crop by knapsack spraying during 3 consecutive days. The findings of the study were as follows: exposure of uncovered hands and of the skin of the back to the concentrate was visually observed during the filling, and respectively loading operations; During spraying exposure from airborne diluted formulation occurred; in addition contamination of the lower parts of the body took place because of direct contact with the sprayed crop; Determination of the amount of the urinary metabolite dimethylphosphate excreted in 24 hours urine samples demonstrated absorption of monocrotophos into the body of the spraymen. The half-life of elimination of the urinary metabolite from the body was on average 18 hours; No clinically significant inhibitions of whole blood or red blood cell cholinesterase activities were found, i.e., 30% below baseline values. However, 8 of 21 spraymen had plasma cholinesterase levels below 50% of baseline values;--No acute adverse health effects associated with the application of monocrotophos were observed, which was in accordance with the absence of clinically significant cholinesterase depressions. The conclusion of the study was that the use of monocrotophos under prevailing typical conditions in the Philippines, which varies from a frequency of one application per season to a maximum of 3 applications each on 3 consecutive days per week, and where label safety instructions are not necessarily observed, is not expected to pose an acute health risk under the prevailing conditions and practices, which includes filling, spraying and cleaning activities. From the experience in this study it is clear that proper spraying technique and adequate use of personal protection will significantly reduce exposure. As such a reduction is highly recommendable, advice on proper spray procedures and adequate personal protection has been reinforced.