US Environmental Protection Agency Finds Low-Risk
November 3, 2003
US Environmental Protection Agency Finds Low-Risk
in Beneficial Reuse of Biosolids
By Rich Anderson
EPA has announced a final determination that biosolids (treated sewage sludge) does not warrant further regulation in a Federal Register Notice (October 24, 2003: 68 Fed. Reg. 61,084). After years of review, the Agency found that treated biosolids that are land applied as a fertilizer and soil conditioner, a common municipal practice, pose very little risk to human health, the environment and wildlife if managed according to existing regulations. The final action by EPA was the result of a rulemaking effort proposed in 1999 as the result of a Court settlement dating back to the early 1990s.
Public Concerns over Dioxin in Biosolids (Treated Sewage Sludge)
EPA adopted regulations governing the use and disposal of sewage sludge in 1993. Those regulations involved performance standards for sludge that is treated and called biosolids. The standards set limits on the concentrations of metals in biosolids that could be land applied so they would not harm humans, animals or the environment. The 1993 standards also addressed pathogens associated with sewage sludge, and the standards required sludge generators to treat the sludge to dramatically reduce or eliminate pathogens before reusing the material as a biosolids fertilizer.
A series of legal challenges were brought against the Agency after the 1993 regulation was adopted. One of the suits charged that the Agency failed to consider persistent bioaccumulative toxic (PBT) organic pollutants such as dioxins, furans and polychlorinated biphenyls (PCBs). Dioxins are unintentional by-products formed by a variety of combustion processes and chemical reactions, including in some cases natural formation. Around the same time as the legal challenges occurred, EPA began a Dioxin Reassessment effort to update the Agency's scientific knowledge of dioxin and dioxin-like compounds and what potential dangers they might pose to humans and the environment. In a settlement action, EPA agreed to conduct a Round II rulemaking to consider whether further regulations were warranted to control dioxins, furans and PCBs.
Land application of biosolids is a common municipal practice. The beneficial reuse of biosolids has long provided an alternative to the now banned ocean disposal of sludge. It also provides a substantial opportunity to achieve recycling goals. Biosolids land application is one of the most successful forms of recycling in the US because biosolids are one of the few materials that can be recycled in a cost-effective manor and does not rely on subsidies. EPA estimates that 8 million dry tons are generated annually, and approximately 54 percent (4.32 million dry tons) are land applied. Another 28 percent (2.24 million dry tons) are disposed in landfills; 17 percent (1.36 million dry tons) are incinerated; and, 1 percent (0.08 million dry tons) is disposed of in lagoons or sewage sludge-only landfills.
Risks from Dioxin Found to be Low
The Conference of Mayors commissioned a study of the land application practice by the renowned Swedish scientist Dr. Christoffer Rappe of the University of Umea, Sweden, and scientific colleagues from the Carolinska Institute in Stockholm. In a 1999 report, Rappe and colleagues concluded that the incremental contribution of dioxin and dioxin-like substances to humans and the environment did not present a public health threat.
The EPA rulemaking conducted a modern risk assessment and concluded that the practice might be responsible for only 0.003 new cases of cancer each year or 0.22 new cases of cancer over a 70 year span. EPA's risk assessment focused on the farm family (adult and child) who is expected to be a higher risk group than the general population. By way of comparison, EPA usually considers one new cancer case per 10,000 people to 1 new case in one million people to be acceptable risk levels. The EPA analysis resulted in far lower risk estimates.
EPA Finds Dioxin Concentrations in Biosolids Declining
One of the findings reported by the Agency in the final Notice was a decline in dioxin concentrations in biosolids. A 2001 national survey of Publicly Owned Treatment Works (POTWs) "...suggests that dioxins levels in sewage sludge have decreased from 1988 to 2001." EPA also indicated that frequency of samples with relatively high concentrations of dioxins have declined since 1988. Some observers believe that regulations adopted in the 1990s on combustion sources have caused airborne dioxin emissions to decline, and that has had an impact on the declining levels of dioxin in biosolids. Patrick Dyke, a United Kingdom based expert on dioxin sources, reported to the Conference of Mayors that combustion sources deposit dioxin emissions on building and street surfaces. Rainfall then washes the dioxin emissions into the sewer systems and they end up in the sewage treatment plant. Dyke suggests that the treatment plants do not produce dioxins; they are just facilities that dioxins from other sources pass through.
at the treatment plants do not produce dioxins; they are just facilities that dioxins from other sources pass through.