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The following is excerpted from my thesis.
Research was done on Sheffield city topsoils in 2005.
“A model of soil variability ... was applied to 569 measurements of metal concentrations ... in the topsoils of Sheffield ... Each of the 35 spatial outliers that occurred in gardens have concentrations exceeding their Soil Guideline Value for residential land use with plant uptake, highlighting a potentially significant exposure pathway. ... coal and furnace waste at these sites suggests that their dispersal ... represents a significant point contaminant process. ... Cr and Ni showed a significant association with disturbed sites ... in part due to their prevalence in areas of historical steel manufacture. ... Pb concentrations in urban topsoil ... were twice the value in the rural environment ... highlighting a very substantial diffuse Pb load to urban soils.” (Rawlins et al. 2005 p.353)
Sheffield has centuries of mining activity and steel works that has impacted the soil quality both through direct dumping of waste and airborne deposition of contaminants.
According to Richard Clare, “In the ‘70s in Sheffield due to industrial pollution, there was a public health recommendation not to grow food anywhere in the city.” (Worthington 2008)
Complicating the situation is the difficulty in getting reliable recommendations from soil testing. While there are laboratories to get contamination testing done,
“There are no widely available reference materials for bioaccessibility testing validated against human or appropriate animal in-vivo studies. ... For lead, comparing in vitro data with human in vivo data indicated that the in vitro methods used by most of the laboratories in England and Wales underestimate bioaccessibility. ... This is clearly a matter of concern if such test results are used to make decisions within the risk management of land contamination." (Barnes et al. 2007 p.67)
Part IIA of the Environmental Protection Act 1990 requires “... a science based risk assessment which takes account of toxicological information, and site specific ... circumstances” to determine if significant possibility of significant harm (SPOSH) exists. The Act also “requires that local authorities identify contaminated land and ensure that significant risks are dealt with.” (Defra 2008 p.3) DEFRA published a software tool, the Contaminated Land Exposure Assessment (CLEA), to assist local authorities with this. The Act establishes to what degree remediation must occur primarily through a link to planning and development requirements.
The guidance provided by DEFRA is intended to assist local authorities, not the individual, with implementation of the Act. (Defra 2008 p.3) By leaving assessment of contamination primarily up to the planning process, are backyard gardens and existing allotment sites being overlooked? How does the homeowner or allotment holder gain access to CLEA tool for assessment of exposure on allotment sites? (COT 2008 p.1) My queries to the council to determine the extent of compliance have received no reply.
Research done by Dr. Rule, professor of biogeochemistry Loyola University, indicates that,
“Most soil contaminants will bind tightly to the soil particles and will move very slowly to the soil below.” (Rule 2008)
With the increasing interest in urban agriculture in Sheffield, are more of its’ citizens being exposed to existing, unmeasured, contamination of the soils?
“... vegetables, particularly leafy crops, grown in heavy metals contaminated soils have higher concentrations of heavy metals than those grown in uncontaminated soil. (Guttormsen et al. 1995; Dowdy and Larson 1995) A major pathway of soil contamination is through atmospheric deposition of heavy metals from point sources such as: metaliferous mining, smelting and industrial activities. ... foliar uptake of atmospheric heavy metals emissions has also been identified as an important pathway of heavy metal contamination in vegetable crops. (Bassuk 1986; Salim et al. 1992)” (Kachenko and Singh 2004 p.1)
Given the lack of guidance for the individual citizen regarding the risks of food-growing in the city from soil contamination, as well as the evidence that there could very well be significant contamination, it seems prudent to apply the precautionary principle and assume that soils within Sheffield are guilty until proven innocent.
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