Persistent Organic Pollutants in Sewage Sludge: Levels, Sources, and

Chapter 6

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Persistent Organic Pollutants in Sewage Sludge: Levels, Sources, and Trends Bradley O. Clarke* and Nichola A. Porter School of Applied Sciences, College of Science, Engineering and Health, RMIT University, Melbourne, Victoria, Australia 3001 *Corresponding author. Phone: +61 3 9925 1787. E-mail: [email protected]. Address: RMIT University School of Applied Sciences (Bld 3 Level 1), LaTrobe St., Melbourne, Victoria, Australia 3001

All sewage sludges in developed countries contain Persistent Organic Pollutants (POPs) and are a source of these chemicals to the environment when recycling this material to land. Therefore, it is important to understand the risks to human health and the environment from this practice. Over the past thirty years a significant amount of research has focused on this subject and this chapter presents an overview of that research. The chemicals that have been reviewed are polychlorinated dioxins/furans, polychlorinated biphenyls, organochlorine pesticides, polybrominated diphenyl ethers, polybrominated biphenyls and perfluorochemicals. A discussion of levels, sources (if known) and trends of each of the chemical groups is presented. The chapter finishes with a brief review of risk assessment work conducted in the area. Most risk assessments have concluded that there is negligible risk to human health from non-ionic POPs when applying this material to land at concentrations typically observed in contempary sewage sludges. However, assessment of the ecological consequences of sewage sludge land application still remains to be completed. Finally, studies indicate that the concentrations of most POPs in sewage sludge are declining globally, demonstrating the effectiveness of source control in reducing environmental contamination.

© 2010 American Chemical Society In Contaminants of Emerging Concern in the Environment: Ecological and Human Health Considerations; Halden, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 2010.


Introduction The land application of treated sewage sludge (biosolids) is a management option that is favoured in most countries throughout the world (1–3), as it takes advantage of the positive fertilizer and soil ameliorating properties of the material (4, 5). However, sewage sludge can be contaminated with Persistent Organic Pollutants (POPs) and it is important to understand the risks to human health and the environment when applying biosolids to land. This topic has been the subject of considerable scientific and regulatory attention over the past thirty years (6–10) and this chapter presents an overview of that research. POPs refer to organic compounds that are environmentally persistent, accumulate in tissues of humans and wildlife, are toxic, and capable of long-range atmospheric transport. Therefore, they pose a significant threat to human health and the environment (11). To address this problem, the United Nations Environment Programme (UNEP) Stockholm Convention on Persistent Organic Pollutants was developed in 2001 to restrict and ultimately eliminate the production, use, release and storage of POPs (11). There were twelve original POPs that included ten intentionally produced compounds (aldrin, chlordane, dichlorodiphenyltrichloroethane (DDT), dieldrin, endrin, hexachlorobenzene (HCB), mirex, polychlorinated biphenyls (PCBs), toxaphene) and two un-intentionally produced classes of compounds [polychlorinated dioxins (PCDD) and polychlorinated furans (PCDFs)]. This has since been augmented to include specific polybrominated diphenyl ethers (PBDEs), polybrominated biphenyls (PBBs), perfluorooctane sulfonic acid (PFOS), pentachlorobenzene, lindane (including α,β hexachlorocyclohexane (HCH) isomers) and chlordecone (12–15). Regulatory authorities in many countries, including Australia, Austria, Czechoslovakia, Denmark, France, Germany and Sweden, consider that land applying sewage sludge contaminated with POPs poses a risk to human health and/or the environment. As a result, they have instigated contaminants limits for various chemicals such as organochlorine pesticides (OCPs), PCBs and PCDD/Fs when recycling sewage sludge to land (1, 2). However, there is not an internationally consistent approach taken to determine how contaminant limits are derived or if indeed they are warranted to protect human health or the environment when applying sludge to land (2, 3). A common consideration when assessing historical scientific studies is the improvement in analytical techniques. The analysis of organic pollutants in sewage sludge is challenging and requires an appropriate extraction, clean-up and quantification technique, each of which has evolved and improved through the years. The early studies utilized packed column chromatography (with quite low resolution by today’s standards) and were later replaced with capillary column chromatography, referred to as High Resolution Gas Chromatography (HRGC). Similarly, the non-specific Electron Capture Detector (ECD) was replaced in later studies with Mass Spectrometry (MS), which provided the analyst with greater confidence in the identity of the analyte and reduced problems associated with interfering compounds. These advances have aided researchers in achieving lower detection levels and greater levels of precision. It is possible that the 138 In Contaminants of Emerging Concern in the Environment: Ecological and Human Health Considerations; Halden, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 2010.


concentrations reported in earlier studies are not accurate, as quite significant variation in the measurement of the same samples can be found even in modern inter-laboratory studies (16). The aims of this review are to summarise international research conducted into POPs in sewage sludge, to assess the significance for use as a fertilizer and soil ameliorant in agriculture and provide a resource for the professionals in the international water industry. The chemicals that will be discussed in the review are: • • • • • •

Polychlorinated dibenzo dioxins and furans Polychlorinated biphenyls Organochlorine pesticides Polybrominated diphenyl ethers Polybrominated biphenyls Perfluorochemicals

A review of literature on the research focusing on each of these classes of compounds is presented in this chapter. Each section discusses levels, trends and sources of these compounds to sewage sludge. Finally, a brief overview of risk assessment studies when land applying sewage sludge is provided.

Table I. Chemical structure and properties of UNEP Persistent Organic Pollutants Compound

Chemical Structure

Chemical Properties

Aldrin

CAS No: 309-00-2 Formula: C12H8Cl15 Mw: 365 g mol-1 Log KOW: 5.30 Vp: 0.003 Pa (20 °C) Reference: (73, 179)

Chlordane

CAS No: 57-74-9 Formula: C10H6Cl18 Mw: 409.83 g mol-1 Log KOW: 4.58 – 5.57 Vp: 0.001 Pa (20 °C) Reference: (73, 179)

Dieldrin

CAS No: 60-57-1 Formula: C12H8Cl16O Mw: 381 g mol-1 Log KOW: 3.69 – 6.2 Vp: 0.00002 Pa (20 °C) Reference: (73, 179) Continued on next page.

139 In Contaminants of Emerging Concern in the Environment: Ecological and Human Health Considerations; Halden, R.; ACS Symposium Series; American Chemical Society: Washington, DC, 2010.

Table I. (Continued). Chemical structure and properties of UNEP Persistent Organic Pollutants


Compound

Chemical Structure

Chemical Properties

DDT


Heptachlor

CAS No: 76-44-8 Formula: C10H5Cl17 Mw: 373.34 g mol-1 Log KOW: 4.4 Vp: 0.0004 Pa (20 °C) Reference: (73, 179)

Hexachlorobenzene

CAS No: 118-74-1 Formula: C6Cl6 Mw: 284.8 g mol-1 Log KOW: 3.93 – 6.42 Vp: 0.0014 Pa (20 °C) Reference: (73, 179)

Lindane


Polybrominated diphenyl ether (PBDE)

CAS No: Varied Formula: C12H(10-x,y)Brx,yO Mw: 248.9 – 959.22 g mol-1 Log KOW: 5.74 – 10 Vp: 0.1 – 1 × 10-6 Pa (25 °C) Reference: (180–182) Note: Ranges are given for mono to deca-BDEs

Polybrominated biphenyl (PBB)

CAS No: Varied Formula: C12H(10-x,y)Brx,y Mw: 232.9 – 943 g mol-1 Log KOW: 4.59 – 8.58 Vp:

Persistent Organic Pollutants in Sewage Sludge: Levels, Sources, and

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