Guidance Document:
Potential for
Exposure to Polychlorinated Dibenzo-p-dioxins and
Dibenzofurans when Recycling Sewage Biosolids on Agricultural Land
British Columbia Ministry of Water, Land and Air Protection Environment Canada 26apr02
This study contributes to the Georgia Basin Ecosystem Initiative, a partnership that provides tools, support and a framework for action towards sustainability in the Georgia Basin.
Prepared for: BC Ministry of Water, Land and Air Protection Environment Canada April 26, 2002
Karen Rideout1, Kay Teschke1,2, Sunil Varughese1
1 School of Occupational and Environmental Hygiene, Faculty of Graduate
Studies, University of British Columbia
2 Department of Health Care and Epidemiology, Faculty of Medicine, University of
British Columbia
Executive summary
The purpose of this review was to develop a set of recommendations to assist British Columbia Medical Health Officers in assessing whether the application of biosolids to various types of agricultural lands would result in increased exposure to polychlorinated dibenzo-p-dioxins and dibenzofurans (dioxins and furans; PCDDs and PCDFs).
The literature review was conducted in three stages. The BC Ministry of Water, Land, and Air Protection provided a set of 50 papers and 44 references, which were assessed for relevance. These were supplemented by a search of the peer-reviewed literature using major medical, toxicological, agricultural, and environmental science databases. Finally, additional papers were collected from a review of the references provided in the articles already collected. Papers were sorted using titles and abstracts; those articles reporting empirical data relating to dioxins and furans in biosolids or soil or to the uptake and transfer of dioxins and furans from soil or feed to crops or animals were collected and reviewed in detail. In total, 56 papers were identified as relevant sources of data relating to dioxins and furans in biosolids, soil, or food products. The results of these empirical studies were used to estimate the potential effect of land application of biosolids on plant or animal tissue concentrations. Because of the many assumptions required, pathway modeling was not conducted as part of this review. However, the results of our review of the empirical studies were compared to those of studies which conducted deterministic modeling.
Studies of dioxin and furan contamination of sludge and soil indicated the following:
- Dioxin and furan levels in municipal sewage sludge ranged from 0.0005 to 8300 pg TEQ/g, with a mean of 81.4 pg TEQ/g. The concentrations of dioxins and furans in sewage sludge illustrated a declining trend over time.
- Background dioxin and furan levels in soil in rural and urban areas ranged from 0.003 to 186 pg TEQ/g, with a mean of 3.7 pg TEQ/g.
- In sludge-amended soil samples, dioxin and furan levels ranged from 1.4 to 15 pg TEQ/g, with a mean of 5.8 pg TEQ/g. Studies that examined levels in treated soil before and after sludge treatment found 1.4 to 17- fold increases in the levels of dioxins and furans after biosolids application.
The data that examined the relationship between dioxin and furan levels in soil and plant foods were limited. Most studies used highly contaminated soils with much higher levels of dioxins and furans than would be found in agricultural land treated with biosolids. The evidence showed:
- Weak positive relationships between soil and plant contamination levels in unpeeled root crops, leafy vegetables, tree fruits, and hay, and little or no associations for peeled root crops, peas and beans, grass, or herbs. Stronger relationships were observed for plants of the cucumber family. In all cases, very large increases in soil PCDD/F concentration (due to experimental contamination) were required to achieve a measurable increase in plant contamination. At soil PCDD/F concentrations associated with biosolids application, the expected increase in plant concentration would be minimal.
There was very little data available to assess the effect of dioxins and furans in land-applied biosolids on the contamination levels in animal tissues and cow’s milk. The body burden in animal tissues and excretion of dioxins and furans in milk is highly dependent on the duration of exposure through the diet; the feeding studies were not of sufficient duration for animal tissue concentrations to reach steady state. The evidence to date showed:
- a positive relationship between dioxins and furans in feed and the concentrations found in the fat of cattle tissues, a much stronger effect than seen in crops, consistent with the expected bioaccumulation in animal tissues; and
- no association between feed contamination and dioxins and furans in milk; however, these compounds are known to be excreted in milk.
The above-described conclusions, based on empirical data, are consistent with the results of published pathway modeling studies for both plants crops and animal tissues. Based on these limited data, application of biosolids to agricultural land used for certain crops (leafy vegetables, tree fruits, peas and beans, harvested forage crops) could be permitted. To ensure that the data derived from studies of highly contaminated soils can be reasonably extrapolated to soils with low contamination levels, a monitoring program is recommended to determine whether dioxin and furan contamination of these foods increases in biosolids-treated land under actual growing conditions.
It is recommended at this time that biosolids application not be permitted on land used to grow plants of the cucumber family or on grazing lands.
The data suggest that different plants have differing potentials for uptake of dioxins and furans, based on the different coefficients for the relationships between soil contamination levels and plant concentrations (listed below in order of increasing association).
- Herbs 0.0001 pg TEQ/g (dry weight) in plant/ pg TEQ/g in soil
- Potatoes 0.0004* pg TEQ/g (dry weight) in plant/ pg TEQ/g in soil
- Hay 0.0008 pg TEQ/g (dry weight) in plant/ pg TEQ/g in soil
- Peas and beans 0.0008 pg TEQ/g (dry weight) in plant/ pg TEQ/g in soil
- Tree fruits 0.0016 pg TEQ/g (fresh weight) in plant/ pg TEQ/g in soil
- Carrots 0.0027* pg TEQ/g (dry weight) in plant/ pg TEQ/g in soil
- Leafy vegetables 0.0042 pg TEQ/g (dry weight) in plant/ pg TEQ/g in soil
- Cucurbitaceae family 0.019* pg TEQ/g (dry weight) in plant/ pg TEQ/g in
soil
* = statistically significant regression coefficient, p < 0.05
Mindfully.org Note: Pumpkins and the melon family are cucurbitaceae. There are about 120 genera and 735 species of Cucurbitaceae worldwide.
Conclusion
In conclusion, it is important to note that there is a great need for further data on the relationship between biosolids application to agricultural land and the PCDD/F concentration of crops and animal food. If human exposure to dioxins and furans is to be minimized, however, it is also essential that the levels of these contaminants in biosolids be reduced. Even if the impact of land-applied biosolids on exposure through food is small, minimizing the PCDD/F content of biosolids will further reduce human exposure and minimize bioaccumulation of these persistent compounds in the environment.
Figure 2. PCDD/F concentrations in sewage sludge.
The red lines indicate the current Canadian guidelines for PCDD/F in agricultural soil, which suggest a maximum of 27 pg TEQ/g soil for unrestricted use and 100 pg TEQ/g soil for restricted use of biosolids on agricultural lands (CH2M Hill, 2001). The blue line indicates the US Environmental Protection Agency (EPA) proposed limit of 300 pg TEQ/g soil for biosolids applied to agricultural lands (US EPA, 1999).
Figure 4. Relationship between PCDD/F concentrations in root crops and soil contamination levels.
This figure includes all values from Tables 5 and 6, with the exception of three measurements in which the soil PCDD/F concentration was much higher (8-fold and 20-fold) (Hulster & Marschner, 1993) than in the other samples and not remotely relevant to the soil concentrations likely to results from biosolids application Data were taken from the following sources: potato (peeled): Hulster & Marschner, 1993; potato tuber: Prinz et al., 1991; Hulster & Marschner, 1993; carrot root: Prinz et al., 1991; Schroll & Scheunert, 1993; carrot peel: Muller et al., 1994.
Figure 8. PCDD/F concentrations in animal tissue when consuming contaminated feed.
This figure includes all values from Table 11 relating to PCDD/F concentration in tissue (not milk), with the exception of studies that did not provide the feed PCDD/F level (Schecter et al., 1994; Winters et al., 1996; Fiedler et al., 1997; Feil & Ellis, 1998; Thorpe et al., 2001), and all values from Table 12, with the exception of one study that used an experimental dose 87 times× higher than in the other studies (Jones et al., 1989; Thorpe et al., 2001). Data were taken from Jensen et al. (1981); Jilg et al. (1992); Richter & McLachlan (2001).
Table 15. Potential change in PCDD/F concentration in root vegetables when grown in different soil concentrations.
A Soil PCDD/F concentration (pg TEQ/g)1 x B Potato tuber concentration (pg TEQ/g dw) y = 0.0004x + 0.3291* C Upper 95% confidence limit—potato tuber (pg TEQ/g dw) y = [0.0004 + (1.96)(0.000063)]x + [0.3291 + (1.96)(0.1331)] D Carrot root concentration (pg TEQ/g dw) y = 0.0027x + 0.3283* E Upper 95% confidence limit—carrot root (pg TEQ/g dw) y = [0.0027 + (1.96)(0.000608)]x + [0.3283 + (1.96)(0.2469)] A B C D E 5 0.33 0.59 0.34 0.83 10 0.33 0.60 0.36 0.85 15 0.34 0.60 0.37 0.87 30 0.34 0.61 0.41 0.93 160 0.39 0.67 0.76 1.43 230 0.42 0.71 0.95 1.71 1250 0.83 1.24 3.70 5.68 1 Soil concentration values are intended to represent the following potential scenarios:
Table 18. Potential change in PCDD/F concentration in forage crops when grown in different soil concentrations.
A Soil PCDD/F concentration (pg TEQ/g)1 x B Hay concentration (pg TEQ/g dw) y = 0.00079x + 3.331 C Upper 95% confidence limit—hay (pg TEQ/g dw) y = [0.00079 + (1.96)(0.000703)]x + [3.331 + (1.96)(1.979)] D Herb concentration (pg TEQ/g dw) y = 0.00011x + 0.3757 E Upper 95% confidence limit—herbs (pg TEQ/g dw) y = [0.00011 + (1.96)(0.00006)]x + [0.3757 + (1.96)(0.1690)] A B C D E 1 3.33 7.21 0.38 0.71 5 3.33 7.22 0.38 0.71 10 3.33 7.23 0.38 0.71 15 3.33 7.24 0.38 0.71 30 3.33 7.27 0.38 0.71 160 3.33 7.56 0.38 0.74 230 3.33 7.71 0.38 0.76 1250 3.33 9.92 0.38 0.99
Table 19. Potential change in PCDD/F concentration in animal tissue when consuming contaminated feed.
A Feed PCDD/F concentration (pg TEQ/g)1 x B Tissue concentration (pg TEQ/g dw) y = 1.458x* C Upper 95% confidence limit—animal tissue (pg TEQ/g dw) y = [1.458 + (1.96)(0.278)]x A B C 0.1 0.1 0.2 0.2 0.3 0.4 0.3 0.4 0.6 0.4 0.6 0.8 0.5 0.7 1.0 1.0 1.5 2.0 2.0 2.9 4.0 3.0 4.4 6.0 4.0 5.8 8.0 5.0 7.3 10.0 10.0 14.6 20.0 25.0 36.5 50.1 41.0 59.8 82.1 1 Soil concentration values are intended to represent the following potential scenarios:
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