Analysis of pesticides in surface water in remote areas in Vietnam: Coping with matrix effects and test of long-term storage stability

Abstract

During the last years, the increased use of pesticides and growing awareness of associated environmental and health problems have led to the implementation of various monitoring programmes in South-East Asia. The introduction of numerous new active ingredients and commercial pesticide formulations in connection with reports on pesticide-related health problems strongly indicate that the analytical procedures should be tested and evaluated for currently used pesticides. Coping with matrix effects and ensuring pesticide stability when samples are taken in remote areas are paramount. In the present study, we tested an analytical method that targets nine currently used pesticides in surface water in northern Vietnam. The method consists of solid phase extraction, storage at −18°C in the adsorbed state, and capillary gas chromatography with nitrogen-phosphorus-detection of five insecticides (dichlorvos, fenobucarb, dimethoate, fenitrothion, and chlorpyrifos), three fungicides (chlorothalonil, metalaxyl, and edifenphos) and one herbicide (atrazine). We evaluated the potential analytical bias caused by matrix effect and investigated its possible causes. We also tested the long-term stability (up to 9 months) of pesticides adsorbed to Carbopack SPE cartridges when stored at temperatures below −18°C. Adopting a matrix-matched calibration technique considerably improved the recovery values of seven of the nine tested pesticides. At spiking levels of 0.1 µg L⁻¹ and 1 µg L⁻¹ and after storage of 119 days at −18°C, recovery values of these pesticides ranged from 67% to 107% and from 67% to 155%, respectively. For the remaining two pesticides recovered at 53–55% at both spiking levels – dichlorvos and chlorothalonil – the method could still be useful for semi-quantitative analysis or as a screening tool. Even though the general recommendation is to minimise storage time to reduce pesticides degradation, our results showed that storage times up to nine months can be adopted for atrazine, metalaxyl, fenitrothion, and chlorpyrifos.

Keywords:

• pesticide analysis
• matrix effect
• SPE
• storage stability
• water matrix

Acknowledgements

The present study was conducted within the framework of the Collaborative Research Centre 564 ‘Sustainable Land Use and Rural Development in Mountainous Regions of Southeast Asia’ funded by the German Research Foundation (Deutsche Forschungsgemeinschaft, DFG). The authors would like to thank Dr Frank for his support in the preparation of this paper.