Summary of Soil Amendment Testing at Trail, British Columbia (2000)

The purpose of these studies, conducted from 1997 through 1999, was to determine whether the lead in Trail soils could be rendered less available to children by adding something to reduce its solubility in the human gastrointestinal tract. The first three phases were each described in separate reports, which are briefly summarized in this final report. Phase one through three involved laboratory testing of potentially effective soil amendments with soil samples from Trail. Based on these tests, three soil amendments were selected for testing in the field in Trail – two commercially available amendments with proprietary chemical compositions, and one “homemade” amendment consisting of phosphorous and iron filings, which was developed through the laboratory testing phases. 

The field investigation found that the only amendment which appeared be effective was one of the proprietary commercial products, which reduced lead bioaccessibility by 15-30 percent. In this field trial, each of the three amendments failed to produce the results that had been observed in the bench-scale trials in the laboratory. Thorough consideration of the differences between the field and laboratory trials led to the conclusion that the most likely explanation for the poor results in the field was that in the laboratory, the amendments were well mixed with water, to the point of forming a slurry, whereas in the field, the amendments were physically mixed into the soil plots, and then water was applied overtop and allowed to infiltrate into the soils. The limited mixing of water, soil and amendments in the field may not have provided adequate contact between the amendment chemicals and the lead minerals in the soils to achieve the reactions desired. 

These studies were conducted because it was considered possible that amending soils with chemicals could be a more cost effective and less disruptive method of addressing lead in Trail soils. It became apparent from these trials that the effectiveness of soil amendments may not be sufficient and that the degree of disturbance required to apply them to residential yards might be nearly as high as that required for soil replacement. If soil amendments could only achieve less than 50 percent reduction in bioaccessibility, and only through excavation of soil, thorough mixing with water and amendments, and replacement in the yard as a saturated slurry, they clearly would not represent an acceptable approach.

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