Prioritisation of EOCs in drinking water : a South African perspective

Abstract

The quality of water in the environment has decreased significantly over the years due to the continuous introduction of various anthropogenic and emerging organic contaminants (EOCs). These contaminants often stem from industrial activities such as agriculture, chemical manufacture, and mining processes, which discharge contaminants directly or indirectly into water systems. The inability of wastewater treatment plants to adequately treat wastewater leads to the discharge of effluents highly concentrated with EOCs, exacerbating the deterioration of water quality resources. Due to the prevalence and persistence of EOCs in surface water, there is a potential for these contaminants to be found in drinking water. The detection of EOCs in drinking water is of growing scientific concern. EOCs may pose risks to human health upon exposure via drinking water, particularly over a lifetime of consumption, especially when these EOCs have no regulatory standards and guideline values. Health effects posed by emerging contaminants in drinking water include carcinogenicity and reproductive toxicity, endocrine disruption, resistance towards antibiotics and promotion of chronic diseases like diabetes. Therefore, these contaminants must be monitored regularly for their presence in drinking water as a mitigation towards their management and control. This research study aimed to develop a prioritisation approach for EOCs of concern that may be present in drinking water and are relevant in the South African context. EOCs were prioritised using a generic risk assessment methodology initiated by conducting a probability assessment. A literature review was conducted to identify contaminants that may be present in surface and drinking water in South Africa. Contaminants were prioritised based on individual criteria: probability assessment, physicochemical properties, toxicity, and an assessment of available international and national regulatory standards. Data used in the individual criteria was sourced from a literature review and from the chemistry database, PubChem, in which the Hazardous Substances Data Bank (HSDB) was the preferred source. A scoring system was then developed to rank the listed compounds. The final prioritisation encompassed the sum of the criteria, generating an overall effect score. The scoring system was qualitative, and the Precautionary Principle was applied to score the individual contaminants. Benzene for example, which ranked first in the final high-priority list, received a score of seven under the probability assessment, a score of 23 for the sum of the physicochemical properties criteria, a score of 20 for the toxicitycriteria, and a score of 10 for the standards and regulations criteria, thus yielding an overall score of 60 from the sum of the criteria. A total of 165 contaminants were ranked in the high-priority list of contaminants in the final prioritisation process, from the compiled final list of 509 contaminants. 131 of the 165 contaminants in the final high-priority contaminants list were detected in the South African water environment, either in surface water or in drinking water, thus making them of relevance in the South African context. Pesticides dominate the high-priority list, with 78 pesticides listed, followed by pharmaceuticals and personal care products (PPCPs) with 48 contaminants. Notably, 48 of the high-priority contaminants have no international or national guideline values and regulatory standards, wherein the top five included the pesticide nitrobenzene and four PPCPs, namely cyclophosphamide, chloramphenicol, oxazepam, and cocaine. This prioritisation study will aid in developing and implementing monitoring programmes for contaminants of concern in drinking water. Only the relevant contaminants of concern should be incorporated into monitoring programmes, thereby ensuring the best allocation of finance and resources for monitoring programmes. Moreover, the prioritised contaminants should give direction to policy and regulation makers in the water sector on the development of regulatory standards and limits. Drinking water institutions may also benefit from the results of this study by using the prioritised contaminants to develop operational limits for the high-priority contaminants.