Questions over herbicide classification
The organochlorine 2,2-dichloropropionate, also known as dalapon, is a herbicide that’s regulated in potable water in Australia, but it is also a little known disinfection by-propduct (DBP). Typical levels when formed as a DBP and their relationship to other DBPs are virtually unknown.
Scientists in Australia sampled potable water samples from a major treatment plant in south east Queensland over 13 weeks. The plant uses chlorination followed by chloramination for disinfection. Chlorine has been employed as a disinfectant for over 100 years and forms hundreds of different DBPs including trihalomethanes, haloacetic acids and N-nitrosamines.
The team found that dalapon concentrations between 0.1 and 0.5 mg l-1 were found in all treated samples. These levels are above the European Union MCL for pesticides in drinking water. However, during this period, dalapon could neither be detected in the immediate source water for the plant, nor at four sites upstream. This, together with the fact that temporal concentration trends during the sampling period mirrored those of trihalomethanes, but at least an order of magnitude lower, suggest in situ formation as a DBP. In this situation then, the compound should be regarded as a DBP, rather than a herbicide contaminant.
Original publication: D W Hawker, J L Cumming, A Watkinson and M E Bartkow, J. Environ. Monit., 2011.
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