Services: Research and Development, Human Health Risk Assessment
Summary: This research programme increased the knowledge base regarding uptake of HCBD, enabling a better understanding of exposures to this compound in the environment
During discussions with the public and within the Weston Quarries Incident Team, questions were raised concerning the potential for human exposure to HCBD (1,1,2,3,4,4-hexachlorobuta-1,3-diene; CAS no. 87-68-3) by uptake from soil into crop plants grown in gardens at Weston Village.
It was recognised that relatively little was known about plant uptake of volatile and semi-volatile chlorinated organic compounds and the client had therefore, commissioned the Institute of Environmental Science, University of Wales, Bangor to undertake a literature review on the potential for the accumulation of chlorinated hydrocarbons, particularly HCBD, in edible vegetation (Jones & Farrar, 2000). Consequently, a focussed laboratory study was initiated to investigate the rate and extent of uptake of HCBD from soil by edible plant species.
The experimental programme successfully evaluated the potential uptake of HCBD at two initial spiked concentrations, and from two soil types, by lettuce and carrot. Plants were cultivated in specially constructed experimental growth chambers and monitored closely to check plant health, soil moisture and temperature. All pots from the chambers were sampled for soil and vegetable tissue samples.
A semi-quantitative mass balance of the HCBD in the experimental system was achieved.
Three empirical models (Briggs-Ryan; Travis & Arms; Topp) were retained for evaluation against the experimental data. Results were presented to the client. For carrot cores, it was concluded that the Briggs-Ryan equation provided a good fit to the experimental data and this model is recommended for use in assessing uptake of HCBD by root crops. For lettuce, none of the empirical models fitted the experimental data.
Both lettuce and carrot seedlings were unaffected by HCBD at the concentrations employed in the experimental programme. Development of the plants in this investigation was affected by the high temperature excursions and the short growing period dictated by the project programme – at the time of harvest, carrot roots were small and a compact lettuce core had not developed. It is not clear what impact these growing conditions may have had on the uptake of HCBD from soil into roots.
ESI is recognised as a UK centre of excellence for groundwater modelling, and is contracted by both public and private organisations to carry out similar work.