Investigating the levels and trends of organochlorine pesticides and polychlorinated biphenyl in sewage sludge

Abstract

A study was completed to investigate temporal trends of organochlorine pesticides (OCPs; aldrin, chlordane, dieldrin, heptachlor, hexachlorbenzene, and DDT) and polychlorinated biphenyls (PCBs) in sewage sludge. Between 2004 and 2006 the concentration of OCPs and PCBs in Australian sewage sludge (n = 829) was consistently < 1000 μg kg^− 1 dry solids DS. Dieldrin, chlordane and DDE were detected in 68%, 27% and 13% at maximum concentrations of 770, 290 and 270 µg kg^− 1 DS, respectively.

Time series analysis (1995–2006) of OCPs and PCBs sewage sludge concentrations (n = 2266) taken from six wastewater treatment plants (WWTPs) of the same geographic region found that lindane, aldrin HCB, heptachlor, DDT, DDD and PCBs were infrequently detected (< 8%). A correlation between dieldrin and chlordane levels was found (P < 0.05) which provides evidence of similar environmental mechanisms facilitating movement of dieldrin and chlordane through environment compartments. It has taken more than 10 years for dieldrin and chlordane to reduce to less than detectable concentrations in freshly generated sewage sludge in Australia following government restrictions.

Internationally, reported sewage sludge OCP concentrations were consistently low and often less than detection limits. Therefore, OCPs are not considered to be a contaminant of regulatory concern for countries that phased out OCP use several decades ago. Concentrations of PCBs in sewage sludge were also consistently low and rarely exceeded European contaminant limits and therefore, regulatory limits may warrant review. The authors recommend that Australian authorities revise regulatory requirements for OCP and PCBs contaminant levels in sewage sludge destined for beneficial reuse as biosolids.

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.