BIOAVAILABILITY AND SPECIATION OF ARSENIC IN CARROTS GROWN IN CONTAMINATED SOIL

Carrots were grown in seven experimental plots (A-G) containing mixtur es of arsenic-contaminated and uncontaminated soil at concentrations r anging from 6.5 to 917 mu g g(-1) (dry mass). The carrots harvested fr om plots A-D (6.5-338 mu g g(-1) arsenic in the soil mixtures) showed a gradually increasing depression of growth with increasing level of c ontamination, At the experimental plots E-G with soil arsenic concentr ations above 400 mu g g(-1) no carrots developed. Whether this effect was caused by arsenic or the concomitant copper content which ranged f rom 11 to 810 mu g g(-1) in the soil mixtures is unknown. The arsenic species extracted from the soils and carrots were separated and detect ed using anion-exchange HPLC coupled with ICP-MS, In the less contamin ated soils from plots A and B arsenite (As-III) was more abundant than arsenate (As-V) in the soil using 1 mmole l(-1) calcium nitrate as ex tractant, In the soils from plots C and D however, As-V dominated over As-III whereas in the corresponding carrots As-V and As-III were foun d at similar concentrations, Methylated arsenic species were sought af ter but not detected in any of the samples. The soil-to-carrot uptake rate (bioavailability) of arsenic was 0.47 +/- 0.06% (average +/- one standard deviation) of the arsenic content in the soils from plots A-D , In contrast to arsenic, the increasing copper content in the soils f rom plot A through D was not available to the carrots as the concentra tion of this element did not increase with increasing soil copper cont ent. The ingestion of the potentially toxic inorganic arsenic via cons umption of carrots grown in soil contaminated at 30 mu g g(-1) in arse nic (plot B) was conservatively estimated at 37 mu g week(-1). This wa s equivalent to only 4% of the provisional tolerable weekly intake (PT WI) for inorganic arsenic as suggested by the WHO and was therefore to xicologically safe. Consumption of carrots grown in more intensely ars enic-contaminated soils, however, would lead to a higher intake of ino rganic arsenic and is therefore not recommended.