Contamination of allotment soil with lead: managing potential risks to health

In the context of contaminated land, assessing risk involves identifying a source, a pathway and a receptor. We describe how this approach worked in practice following the discovery of high lead levels in the soil of an allotment site in a London borough.

Soil and produce analyses were undertaken. A worst-case scenario was constructed to estimate the maximum potential lead intake by consumers. A questionnaire survey was undertaken of individuals who either worked on the allotment or ate significant amounts of produce grown on it. They were also offered blood lead tests.

High lead levels were found in soil and produce. The worst-case assessment showed that the estimated lead intake by a hypothetical consumer of allotment produce exceeded the provisional tolerable weekly intake almost 10-fold. Further tests on produce indicated that soil contamination had contributed to the high lead levels. The questionnaire survey did not reveal any chronic illness related to lead exposure. Of the five tested, none had raised blood lead levels.

A decision was made to remediate the site. Pending this, we advised the allotment holders not to cultivate the land or eat any produce grown on it as we could not be sure that preparation of the produce before consumption would remove all adherent lead-contaminated soil, and continued cultivation could also expose them to lead in the soil dust.