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Phosphonates are characterised by having two or more -C-PO3H2 groups. AMPA has been shown to be formed as a degradation product of some phosphonates that are not used as herbicides but are used as cooling water additives, detergents and for other industrial applications.

It is therefore important to assess the extent of formation of AMPA from use of these chemicals.

Regarding other phosphonate uses, detergents are considered to be the major use and to result in the major emission to surface waters. It is important to note that not all phosphonates are precursors of AMPA and such chemicals have not been taken into consideration for the calculations. Moreover, the rate of degradation of other phosphonates is slower than that of glyphosate. Information on rate of degradation of glyphosate and of phosphonates is shown below:

In a Dutch report (Staats et al), phosphonates were thought to be responsible for a proportion of the AMPA found in large and regional rivers. This percentage increased slightly in regional rivers during periods of low glyphosate emission (but the resulting AMPA concentrations were a factor of approximately 2 to 6 lower).

A Danish EPA investigation on AMPA (May 1997) concluded that the fate of phosphonates in industrial cleaning equipment had not been clarified. No information on AMPA in wastewater has been obtained so a Water Environment Plan has been put in place which recommended monitoring wastewater, wastewater sludge and rainwater discharge for AMPA.

However, a Consultative Expert Group on Detergents in the Environment in The Netherlands produced a detailed study in 1997 in which the formation of AMPA from phosphonates was reviewed. It was further stated that AMPA concentrations in cooling water from industrial processes was around 14 microg/l. This contrasted to values of 0.04-1.48 microg/l for AMPA in Dutch surface waters generally.

Conclusion

Although there is perhaps less detailed information on formation of AMPA from phosphonates and its subsequent fate, it is clear that AMPA is formed and can enter the aquatic environment not only from glyphosate but also from phosphonate chemicals.

It is therefore essential that in assessing detections of AMPA in natural waters, all potential sources are taken into account when assessing the source of the AMPA.