Glyphosate in surface water
The diverse and intensive use and the wide application window of glyphosate herbicides imply that glyphosate has the potential to reach surface water throughout the year from indirect routes of entry like spray drift, runoff and drainage, as well as point source contamination due to bad agricultural practice. Aminomethylphosphonic acid commonly known as AMPA, the major metabolite of glyphosate in the environment, is commonly included in the surface water monitoring program for plant protection products, particularly because it can be determined by the same analytical method as glyphosate. The results show that AMPA is more frequently found in surface waters than glyphosate, and often at higher levels.
Aminomethylphosphonic acid is the simplest member of a broad class of chemicals known as aminomethylenephosphonates. Members of this class of chemicals include detergent additives and sequestering agents to prevent scaling in boilers and cooling water facilities. Studies provide evidence that detergent additives and sequestering agents, from household and industrial uses, can be a significant source of AMPA 9. They are directly discharged into the environment through drains and/or wastewater effluents, in amounts large enough to contribute significantly to the AMPA load in surface water.
The levels of pesticides and their metabolites in surface water are very often compared to the European Union drinking water trigger of 0.1 µg/L. This value is a threshold resulting from political consensus rather than from scientific evaluation and has therefore no toxicological nor ecotoxicological significance. In order to estimate the risk to the aquatic environment, the measured concentration (exposure) has to be compared to a biological effect value (hazard), which is significantly greater than the drinking water trigger of 0.1 µg/L. In the case of glyphosate and AMPA (a metabolite which is regarded as ‘non-relevant’ 2, the threshold for ecotoxicological concern is >1000 times higher than the drinking water threshold 3, 15 and the risk to the aquatic environment from the levels observed in surface water monitoring programs is negligible. The potential human exposure to surface water is through finished drinking water abstracted from surface water. Numerous studies have shown that glyphosate and AMPA are readily removed by chemical/oxidative disinfections, which are standard surface water treatment processes used for drinking water production 10, 11. Other processes commonly used in water treatment (bankside or dune infiltration, coagulation/clarification/filtration and slow sand filtration) each contribute to the removal, but with a lower efficiency than the disinfection processes.
Because of their low toxicity, the health-based value derived for AMPA alone or in combination with glyphosate is orders of magnitude higher than concentrations of glyphosate or AMPA potentially found in drinking-water. Under usual conditions, therefore, the presence of glyphosate and AMPA in drinking-water does not represent a hazard to human health (WHO, drinking water guidelines, see paragraph 12.65).
Last update: 17 April 2015