Elsevier

Water Research

Volume 183, 15 September 2020, 116066
Water Research

Chlorothalonil transformation products in drinking water resources: Widespread and challenging to abate

https://doi.org/10.1016/j.watres.2020.116066Get rights and content
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Highlights

  • Chlorothalonil transformation products are wide-spread in drinking water resources.

  • Ozone, hydroxyl radicals, activated carbon, UV, and reverse osmosis were tested.

  • Sulfonic acid transformation products are highly persistent during treatment.

  • Only very fresh activated carbon retains the transformation products sufficiently.

  • Reverse osmosis removes all transformation products almost completely.

Abstract

Chlorothalonil, a fungicide applied for decades worldwide, has recently been banned in the European Union (EU) and Switzerland due to its carcinogenicity and the presence of potentially toxic transformation products (TPs) in groundwater. The spread and concentration range of chlorothalonil TPs in different drinking water resources was examined (73 groundwater and four surface water samples mainly from Switzerland). The chlorothalonil sulfonic acid TPs (R471811, R419492, R417888) occurred more frequently and at higher concentrations (detected in 65–100% of the samples, ≤2200 ngL−1) than the phenolic TPs (SYN507900, SYN548580, R611968; detected in 10–30% of the samples, ≤130 ngL−1). The TP R471811 was found in all samples and even in 52% of the samples above 100 ngL−1, the drinking water standard in Switzerland and other European countries. Therefore, the abatement of chlorothalonil TPs was investigated in laboratory and pilot-scale experiments and along the treatment train of various water works, comprising aquifer recharge, UV disinfection, ozonation, advanced oxidation processes (AOPs), activated carbon treatment, and reverse osmosis. The phenolic TPs can be abated during ozonation (second order rate constant kO3 ∼104 M−1s−1) and by reaction with hydroxyl radicals (radical dotOH) in AOPs (kOH ∼109 M−1s−1). In contrast, the sulfonic acid TPs, which occurred in higher concentrations in drinking water resources, react only very slowly with ozone (kO3 <0.04 M−1s−1) and radical dotOH (kOH <5.0 × 107 M−1s−1) and therefore persist in ozonation and radical dotOH-based AOPs. Activated carbon retained the very polar TP R471811 only up to a specific throughput of 25 m3kg-1 (20% breakthrough), similarly to the X-ray contrast agent diatrizoic acid. Reverse osmosis was capable of removing all chlorothalonil TPs by ≥98%.

Keywords

Pesticide
Metabolite
Water treatment
Groundwater
Ozonation
Activated carbon

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