Catch Me If You Can: Chemical Adulteration in Wastewater Compliance Testing

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A new legislative framework issued by the Ministry of Ecology and Environment of China prohibits any intentional use of ‘interfering agent’ during wastewater compliance testing. For the first time, such practices are brought to public attention, although they have been barely discussed in scientific literature. Targeting the dichromate method in chemical oxygen demand (COD) testing, a standard method widely adopted by regulatory agencies, the sodium chlorate-based ‘COD remover’ lowers measurements by oxidizing organic pollutants in samples under acidic and high-temperature conditions. Based on its reactions, the interfering agent only works under the testing conditions, and does not function as an effective treatment in wastewater under normal conditions. The use of ‘COD remover’ may have created an underground industry, where users can anonymously purchase those products in 25-Kg packages from all major domestic online retailers in China. A notable case was recently publicized under the new legislation, where 131 tons of ‘COD remover’ had been used in a municipal wastewater treatment plant. However, little is known about the prevalence of its use, in China or other geographic regions, and whether COD is the only targeted indicator in wastewater compliance testing. Nitrites function as interfering agents in the iodometric method for measuring dissolved oxygen in wastewater. There are also reports of chemical adulteration in online monitoring of gas emissions. The specific reactions and mechanisms involved in compliance testing methods provide inherent vulnerability for targeted chemical adulteration. There is a need to develop more robust and adulteration-proof methods for wastewater and other environmental compliance testing.