Investigating the levels and trends of organochlorine pesticides and polychlorinated biphenyl in sewage sludge
Introduction
Many countries have contaminant limits for organic pollutants in biosolids (treated sewage sludge) to assess its suitability for beneficial recycling (i.e. applied to land as a fertilizer). Internationally, Australia is the only country to have contaminant limits for organochlorine pesticides (OCPs), which may be a consequence of a relative recent phasing out of these compounds in the 1990s. Many third-world countries continue to use OCPs for malaria control and this study will provide information regarding the expected length of time that environmental contamination will occur. Similar to Australia, a number of European countries have contaminant limits for polychlorinated biphenyls (PCBs), therefore studies of PCBs in sewage sludge are internationally relevant (European Commission, 2001). Regardless of whether sewage sludge in beneficially recycled, it is an important environmental matrix to monitor for organic chemical pollution.
OCPs are considered to be the second generation of pesticides that took over from the early first generation of insecticides produced from inorganic compounds (arsenic, lead, copper, and sulfur) in the 1940s (Chenier, 2002). The use of these chemicals improved our quality of life by ensuring a regular supply food, as well as protection against insect borne disease. The most infamous OCP, DDT (1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane), was found to be remarkably active against a number of insect pests. Ironically, one of the valued properties of DDT was its persistence, reducing the need for frequent applications. DDT became the prototype OCP from which other more toxic pesticides where developed viz. aldrin, dieldrin, lindane, chlordane and heptachlor. Due to the persistence of many OCPs and their potential impact upon human and wildlife health (as carcinogens and endocrine disruptors), international treaties have been developed to prevent further environmental contamination. Despite restrictions for use in most Western nations, OCPs and their breakdown products are still detected in many environmental compartments, including humans, throughout the world (Erickson, 1997, Zitko, 2003, Harden et al., 2005).
PCBs are one of the great environmental pollutants of the twentieth century. The commercial production of PCBs began in the USA in 1929 and their commercially valued properties were electrical resistance, low volatility and resistance to degradation at high temperatures. The commercial product(s) were a complex mixture of PCB isomers and used for a variety of purposes, such as dielectric fluids in capacitors and transformers. It was not until the 1960s that PCBs were found to accumulate in biota globally, entering the food chain through “the backdoor” (Jensen, 1972). Due to their persistence and potential impact on humans and wildlife (carcinogens, endocrine disruptors) in 2001 they were included in the Stockholm Convention on Persistent Organic Pollutants to prevent further environmental contamination (UNEP, 2001). Even though PCB production has been banned in most countries since the 1970s and 1980s, they are still found in infrastructure throughout the world. It is estimated that over 1 million tonnes of PCBs have been generated and about one third of this quantity is thought to be continuing to circulate in the environment (Birkett and Lester, 2003). PCBs are now ubiquitous environmental pollutants, occurring in human and animal tissue, and most environmental compartments (Erickson, 1997).
This paper presents a literature review of OCPs and PCBs in sewage sludge, detailing the typical concentrations and trends observed internationally. This review is pertinent to countries that have regulatory limits for PCBs in sewage sludge (viz., Australia, Germany) and other countries considering such restrictions (European Commission, 2001). This is followed by data obtained from two Australian monitoring studies that have quantified levels and trends of OCPs and PCBs in Australian sewage sludge and compares them to domestic guidelines and international studies.
Section snippets
Historical levels and sources
A comprehensive examination of the scientific peer-reviewed literature is presented that examines OCPs and PCBs sewage sludge concentrations and sources.
Australian sewage sludge survey 2004–2006
Australian WWTPs must monitor sewage sludge intended for beneficial reuse for OCPs and PCBs. Concentration data (n = 829) was obtained from participating WWTPs (n = 58) that was released to the authors on condition of anonymity. Results are discussed at an aggregate level, organised according to State and year (Table 1). To ensure comparable data,
Organochlorine pesticides
A large volume of research investigating OCPs in environmental compartments has been published; however, few studies of levels and trends in sewage sludge have been published. There has been no review undertaken on this subject internationally and in Australia, no published research could be found. The concentration of OCPs in sewage sludge has been reported from the United States of America (USA), the United Kingdom (UK), Sweden, Italy, Greece and recently, China. A summary of English language
Conclusion
Dieldrin, chlordane and DDE were frequently detected in Australian sewage sludges (n = 829) between 2004 and 2006. They were detected in 68%, 27% and 13% of samples at maximum concentrations of 770, 290 and 270 µg kg− 1 DS, respectively. Many other OCPs were rarely detected and lindane was not detected in any samples in this survey, including in analysis of sludge over ten years from six WWTPs (n = 2266). Again, in sludges monitored for OCPs and PCBs generated from 6 WWTPs of the same geographic
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