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Regulatory Alert - RA 02-14 - NOTICE OF DATA AVAILABILITY ON THE PART 503 STANDARDS FOR LAND APPLIED BIOSOLIDS

Member Pipeline - Regulatory - Alert (RA 02-14)

To: Members & Affiliates, Biosolids Management Committee
From: National Office
Date: June 20, 2002
Subject: NOTICE OF DATA AVAILABILITY ON THE PART 503 STANDARDS FOR LAND APPLIED BIOSOLIDS
Reference: RA 02-14

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Action Please By:
August 23, 2002

On June 12, the U.S. Environmental Protection Agency (EPA or Agency) published a Notice of Data Availability (NODA) on the Part 503 standards for land applied biosolids (67 Fed. Reg. 40554). The NODA summarizes new data on the levels of dioxin in biosolids and EPA’s revised risk assessment for estimating the risks from dioxin and dioxin-like compounds associated with the land application of biosolids. Using the new dioxin data and revised risk assessment, EPA estimates that the lifetime cancer risk to its modeled (highly-exposed) population is within the Agency’s range of acceptable risks. Furthermore, EPA’s revised risk assessment shows no measurable effect on risk if all biosolids were required to meet the Agency’s 1999 proposed limit of 300 parts per trillion (ppt) toxic equivalents (TEQ). The NODA also describes how the Agency-wide Dioxin Reassessment process may affect any final regulatory decision, the screening ecological risk analysis (SERA), and some options EPA is considering for the final rule.

EPA will consider comments received by September 10. AMSA is already working with Cambridge Environmental Inc. to review the new data and the revised risk assessment. In addition, AMSA will work through its Biosolids Management Committee to compile comments on the other components of the NODA. We ask members to provide us with their feedback by August 19, 2002. AMSA is specifically looking for member input on alternatives for monitoring the level of dioxins in biosolids (see below). Comments should be submitted to Chris Hornback, AMSA at chornback@amsa-cleanwater.org. The NODA is available on EPA’s web site at:
http://www.epa.gov/fedrgstr/EPA-WATER/2002/June/Day-12/w14761.pdf.

EPA is under a court-ordered deadline to take final action on the proposed land application rule by October 17, 2003 (see Legal Alert 02-6). EPA met a prior court-ordered deadline of December 15, 2001 for taking final action on its proposal concerning surface disposal and incineration in a sewage sludge incinerator. EPA’s final action found that numeric standards or management practices are not warranted for dioxin and dioxin-like compounds in sewage sludge disposed via these approaches (66 Fed. Reg. 66228; December 21, 2001).

I. Member Comment Requested on Alternatives to a Numeric Regulatory Limit
Using the new dioxin data, EPA’s revised risk assessment estimates that the lifetime cancer risk to its modeled (highly-exposed) population is very low and well within the Agency’s range of acceptable risks. The results of the risk assessment also indicate that a numeric regulatory limit of 300 ppt TEQ, or even 100 ppt TEQ, would not significantly affect the already minimal risk posed by dioxins in land applied biosolids. Although studies conducted by both EPA and AMSA did find high levels of dioxins in some biosolids samples, these elevated concentrations appear to fluctuate and may not be consistently identified. Together, the risk assessment and the transient nature of elevated dioxin concentrations in biosolids suggest that an alternative to a numeric regulatory limit would be more effective. Such an alternative would have POTWs detecting elevated levels of dioxins in their biosolids seek to identify sources contributing to the higher levels.

While EPA’s revised risk assessment indicates that a numeric dioxin limit is unnecessary, AMSA believes it will be important to address elevated dioxin levels where they exist to maintain public confidence in the practice of land application. AMSA is exploring two potential alternatives to a numeric limit that would better address these occasional elevated dioxin levels. Depending on member response, AMSA will offer one or both of the alternatives to the Agency in the Association’s comments on the NODA.

1) AMSA seeks input on whether member agencies would support a voluntary alternative to a numeric limit. This would consist of a periodic, self-monitoring program, combined with a methodology for identifying sources of dioxins, as discussed in the NODA. Such a process would be less burdensome than a national numeric limit, and offer an effective method for POTWs to address site-specific dioxin conditions. Under this option, EPA would take “no regulatory action” for dioxin in land applied biosolids and rely on POTWs to implement the self-monitoring program. The specific level of dioxins in biosolids that might concern a particular wastewater agency would vary. EPA could provide guidance on ranges of dioxin concentrations to trigger POTW review.

2) AMSA also seeks input on an alternative that would require, by federal regulation, periodic monitoring (once every five years) for dioxins in biosolids, but that would not automatically preclude land application if elevated levels of dioxins are found. Rather, if elevated concentrations are detected, POTWs would be required to investigate to confirm the initial test result and to identify the source of the dioxins. This option would still require EPA to stipulate an action level or at least a range of action levels, above which such further investigation would be required. POTWs would decide on the appropriate course of action, which could include temporarily halting land application and working with identified dioxin sources to control discharges.

In addition to suggesting alternatives to a numeric limit, AMSA’s comments will highlight the many conservative assumptions EPA made in conducting the risk assessment. Given the high-end (conservative) nature of the risk assessment, the resulting low risk levels are even more meaningful. Even with a high degree of conservatism built in, current levels of dioxins in land applied biosolids do not present a risk to the general population. AMSA encourages its members to review the assumptions EPA made regarding the management of biosolids, as well as EPA’s list of issues for which the Agency is seeking comment (see page 40575 of the NODA).

II. EPA Responds to Comments on 1999 Proposal
Following EPA’s proposal to limit the amount of dioxin and dioxin-like compounds (dioxins) in land applied biosolids (64 Fed. Reg. 72045; December 23, 1999), the risk assessment that supported the proposed limit of 300 ppt TEQ was peer reviewed in accordance with EPA procedures. Both the peer review comments and the public comments received on the proposal raised significant issues concerning the methodology and assumptions used for the assessment. The public and peer review comments also emphasized the need to collect new data on dioxins in biosolids. AMSA’s comments on the proposal can be obtained on the Association’s web site at:
http://www.amsa-cleanwater.org/private/legreg/outreach/3-23-00AMSAcomments.pdf.

In response to these comments, EPA conducted a survey to update the dioxin information presented in the 1988 National Sewage Sludge Survey, which had been used as the basis for the original proposal. The 2001 EPA Survey included biosolids samples from 94 POTWs selected from the 174 POTWs that had been surveyed in the 1988 study. EPA was also able to compare the results from their 2001 EPA Survey with the results from AMSA’s 2000/2001 Dioxin in Biosolids Survey. AMSA’s survey is available on the web at: http://www.amsa-cleanwater.org/advocacy/dioxin/dioxin.cfm.

The principal comment EPA received concerning the risk assessment methodology was that the Agency should use a probabilistic approach instead of a deterministic approach. The revised risk assessment summarized in the NODA includes a probabilistic methodology for determining exposure to dioxins. The probabilistic analysis captures both the variability in biosolids application practices across the nation and the differences in the environmental settings (e.g., soils, meteorology and agricultural practices) in which biosolids may be land-applied.

New Dioxin Data
The NODA provides a brief analysis of the results from EPA’s 2001 Dioxin Update Survey (2001 EPA Survey). The results are summarized separately for dioxins and furans, coplanar PCBs, and total dioxin-like compounds. EPA presents the results using three alternative substitution values for “non-detects” (zero, one-half the detection limit, and the detection limit). Because of the very low detection limits achieved in the 2001 EPA Survey, there were only very small differences in the summary results for the three substitution methods. (Non-detects were assumed to equal one-half the detection limit for conducting the risk assessment).

The results indicate an average (mean) dioxin concentration of approximately 31 ppt TEQ. For comparison, the AMSA survey found a mean dioxin concentration of approximately 21 ppt TEQ. The 2001 EPA Survey found very small differences in the median dioxin concentration between small and large POTWs, but found substantial differences at the upper percentile ranges, though EPA is uncertain of the significance of these differences due to the relatively small sample sizes and the sensitivity of the results to the treatment of non-detect measurements. The lower levels of dioxins in biosolids from small facilities as compared to large facilities (flow greater than one million gallons per day) support EPA’s proposed exclusion of small entities from any limit on dioxin in biosolids.

EPA also compares the results of its 2001 Survey to the results from the 1988 Survey. The values obtained in the 2001 EPA Survey for the upper percentiles are lower than those obtained in the 1988 Survey, implying a decline in the concentrations of dioxins in biosolids since 1988. EPA cautions that the significance of these differences is not certain given the changes in the sampling procedures and analytic methods since 1988.

In addition, EPA offers observations about the variability of dioxin concentrations that may have implications for the final regulatory standards. Of the 94 POTWs participating in both the 1988 Survey and the 2001 EPA Survey, a total of 14 POTWs have biosolids dioxin concentrations equal to or greater than 93 ppt TEQ from at least one of the surveys. These same 14 POTWs exhibited the greatest differences in dioxins concentrations when comparing the results of the 1988 and 2001 EPA surveys. The other 80 POTWs participating in both surveys have substantially smaller differences. Of the 14 POTWs that exhibited the greatest variation in concentration, four had large increases and ten had large decreases in biosolids dioxin concentrations. Thus, it appears that biosolids with higher concentrations of dioxins may experience a greater variability in dioxin concentration over time and that higher dioxin levels may not remain high for a significant period of time.

These patterns of variability will weigh heavily on EPA’s final regulatory decision. The NODA discusses whether changes in the proposed monitoring scheme would be appropriate given the periodic spikes in concentrations and the transient nature of these higher levels of dioxins.

Revised Risk Assessment
In addition to the new probabilistic methodology for exposure analysis, the revised risk assessment uses new inputs which include a redefined “highly exposed individual,” new pathways and mechanisms of exposure consistent with EPA’s Draft Dioxin Reassessment (discussed in more detail below), a number of new exposure factors adopted from the latest EPA Exposure Factors Handbook, and a sensitivity analysis to determine the relative importance of the input variables.

The new risk assessment evaluated exposure of a farm family that consumes 50 percent of its diet from home-produced crops and animal products grown on their own biosolids-amended land, while the proposal used a rural family consuming a smaller proportion of home-grown products. EPA estimates that the highly exposed farm family population is no greater than 11,000 individuals out of the population of the United States.

Lifetime excess cancer risk estimates are the product of the lifetime average daily dose (the probabilistic exposure assessment estimates delivered doses for each of the dioxin congeners, which are then summed to yield an overall dose) and the corresponding cancer slope factor. Using the Agency’s current cancer slope factor, the high-end individual excess lifetime risk to the highly exposed modeled population could range from 2 x 10-5 to 1 x 10-6 (two in one-hundred thousand to one in one million) for exposure by multiple pathways. This excess risk falls within the range of risks considered by the Agency to be acceptable, 1 x 10-6 to 1 x 10-4.

Additional risk calculations were performed to estimate the impact on the risk if biosolids with 300 ppt TEQ dioxins and 100 ppt TEQ dioxins were restricted from land application. Eliminating these higher concentration biosolids did not change the estimated risk. EPA goes on to state in their characterization of the risk, that continual application of biosolids with significantly higher concentrations of dioxins than currently measured would be necessary to predict quantifiable increases in risk. Despite the spikes in concentration identified in the 2001 EPA Survey, EPA believes that it is highly unlikely that a single family would be exposed to these biosolids with elevated concentrations long enough to produce a quantifiable increase in risk due to the transient nature of the higher concentrations.

Another interesting finding indicates that high-end incremental risk estimates for highly exposed farm families from the land application of biosolids are approximately ten times lower than background risks for the general public.

Given the level of risk and the small size of the highly exposed population (11,000 individuals), EPA estimates the annual number of cancer cases to be 0.006 for the highest exposure percentile (99th percentile).

Screening Ecological Risk Analysis
In response to comments received on the 1999 proposal, EPA performed a screening ecological risk analysis (SERA) to evaluate the potential ecological effects of dioxin in land applied biosolids. SERAs are designed to provide a high level of confidence that there is a low probability of adverse effects to ecological receptors. In other words, a SERA is not designed to provide a definitive estimate of risk, but rather some indication of the potential for ecological risk.

EPA chose the hazard quotient (HQ) as the risk measurement for this SERA. The HQ is essentially a ratio of actual exposure to a benchmark exposure level that is considered safe. If the actual exposure is the same or greater than the benchmark, the ratio equals or exceeds one (1). An HQ of less than one (HQ<1) indicates that the concentration (or dose) of a chemical, in this case dioxins, is below the protective ecological benchmark and therefore passes the screening. An HQ of greater than or equal to one (HQ≥1) indicates a potential for ecological impact.

EPA used a two phased approach to ecological risk, first using a highly conservative approach to determine whether any of the habitats, receptor categories, and exposure routes might be of concern. HQs greater than one (1) in the Phase 1 analysis indicated that a more refined analysis was needed to determine whether ecological effects are expected.

EPA conducted a number of Phase 2 analyses for receptor categories (species) in two major habitats: terrestrial (receptors feeding and foraging in the agricultural fields where biosolids are applied) and waterbody margin habitat (receptors exposed through living in or feeding from nearby surface water bodies that receive dioxin loads through runoff). For the Phase 2 analyses conducted for this SERA, no HQ values exceeded the target HQ of one (1). Values ranged from a minimum of 0.0035 (Canada goose) to a maximum value of 0.36 (short-tailed shrew). The median values for the terrestrial and waterbody margin habitats, 0.044 and 0.015 respectively, indicate that the potential for effects on terrestrial receptors may be somewhat higher than for receptors in waterbody margin habitats. However, EPA noted that none of the Phase 2 values exceeded the protective ecological benchmark of one (1).

III. The Agency-Wide Dioxin Reassessment
Since 1991 EPA has been conducting a scientific reassessment of the health risks associated with exposure to dioxins. EPA began this reassessment in light of new scientific information on the health effects of dioxins and the scientific community’s improved understanding of dioxin toxicity. After more than ten years of development, the Draft Dioxin Reassessment now appears to be approaching completion. While the draft reassessment does not represent Agency policy or factual conclusions, and EPA has not yet issued final findings or conclusions based on the reassessment, much of the information incorporated into the draft reassessment reflects the current state of knowledge with respect to dioxins. Much of this information is incorporated into the NODA.

The Draft Dioxin Reassessment also presents conclusions and findings that are still under review, including the revised cancer slope factor and the use of a margin of exposure (MOE) approach for evaluating the risks of non-cancer health effects from exposure to dioxins. Although EPA has not incorporated this information into the revised risk assessment, the NODA does discuss the potential implications of the information for the Agency’s final regulatory decision on dioxins in land applied biosolids.

The Agency’s draft cancer slope factor is approximately six times more stringent than the current value (used in the NODA). Use of this more stringent cancer slope factor results in risks ranging from
1.2 x 10-4 to 6 x 10-6, still within the Agency’s range of acceptable risks.

IV. Identifying Sources of Dioxins and EPA’s Proposed Methodology
Both the 2001 EPA Survey and AMSA’s 2000/2001 Dioxin in Biosolids Survey found a few biosolids samples that had concentrations of dioxins much higher than what was typically observed. EPA’s analysis of its survey results and comparisons with previous data indicated that these higher levels of dioxins appear to be transient and may not be consistently identified. While EPA acknowledges that the revised risk assessment shows no measurable change in risk from eliminating these “spikes,” the “Agency believes it may be beneficial to develop a procedure to identify the sources contributing to higher levels of dioxins” in biosolids (see page 40575 of the NODA).

EPA seeks comment on a methodology to assist communities in identifying sources of elevated dioxins in their biosolids. The methodology would first entail the identification of sources known to be generators or dischargers of dioxins. This information would primarily come from EPA’s Toxics Release Inventory (TRI), but would also include information from the POTW’s pretreatment program and any community-specific studies that had been conducted. The second element of the methodology would involve a comparison of the mix of the 29 dioxin congeners measured in a biosolids sample to the “fingerprint” of the dioxin congeners for known sources of dioxins. Mixtures of the 29 congeners of dioxins have distinct patterns (fingerprints) of relative proportions for each of the congener classes. In other words, dioxins produced by combustion have a different fingerprint than dioxins produced by chemical processes, such as pulp and paper mill bleaching. Such information would be of potential value to a community in narrowing down the list of possible sources of the dioxins.

V. EPA’s Specific Request for Comments
On page 40575 of the NODA, EPA lists 12 specific elements on which the Agency is soliciting comments. Among other things, EPA seeks comment on the trends identified in the 2001 survey data, a number of the assumptions the Agency made throughout the risk assessment (e.g., choice of the highly exposed farm family, the treatment of non-detects), the methodology used to screen ecological risk, and the finding that a 300 ppt TEQ limit would not make a detectable difference in the risk of cancer to the highly exposed family.

The Agency also seeks comment on taking no action for dioxins in land applied biosolids and the proposed methodology for identifying the sources of dioxins contributing to elevated biosolids concentrations. If AMSA chooses to pursue Alternative 1 (above), we would recommend the Agency take no action for dioxins in land applied biosolids and offer to conduct a voluntary monitoring program, which uses the Agency’s methodology for investigating dioxin sources.

 

If you have any questions about the NODA or AMSA’s efforts to prepare comments on the new data and revised risk assessment, please contact Chris Hornback, AMSA at 202/833-9106 or chornback@amsa-cleanwater.org.