The use of an odour wheel classification for the evaluation of human health risk criteria for compost facilities

Odorants are released during the decomposition of organic waste at compost treatment plants. Composting releases volatile organic chemicals (VOCs), including alcohols, aldehydes, volatile fatty acids, ammonia and other nitrogen compounds, xenobiotic solvents, and various sulphur compounds into the environment as categorised by a compost odor wheel. Each odorant possesses a characteristic odour signature – quality and threshold as well as a toxicity value. This paper presents data relating the human odour detection limit to human health threshold criteria developed by the National Institute for Occupational Safety and Health, Occupational Safety and Health Administration, the United States Environmental Protection Agency Region 9 and the World Health Organisation. This comparison indicates that: (1) the human odour threshold concentrations (OTC) for most compost odorants are far lower than their respective human health risk (regulatory) threshold values, (2) several compost odorants have OTC that are below some of their respective regulatory thresholds and above others (i.e. dimethyl amine, formic acid acetone, ethyl benzene and toluene) and (3) only the VOCs probably present as contaminants in the raw composting material have OTC greater than all of its regulatory thresholds (i.e. benzene). Benzene is the most hazardous VOC associated with composting and should be monitored.