Perchlorate, nitrate, and iodine uptake and distribution in lettuce (Lactuca sativa L.) and potential impact on background levels in humans.

Abstract

Much focus has been placed on the impact of exposure to perchlorate (ClO4(-)) from drinking water. Recently, it has become more apparent that a significant percentage of the total ClO4(-) exposure may be due to ingestion of food. Most studies have only evaluated the uptake and distribution of ClO4(-) by plants without considering the potential for uptake of iodine (I) by the plant and the subsequent impacts on ClO4(-) uptake and distribution on human health. The objectives of this research effort were to evaluate the relative uptake of ClO4(-) and I supplied as either KI or KIO3, the two major environmental forms of I in a standard hydroponic nutrient solution using butter head lettuce. No interaction of ClO4(-) uptake and distribution was found in the presence of I(-) or IO3(-) relative to previous studies evaluating ClO4(-) alone. Bioconcentration factors for ClO4(-) and total I in butter head lettuce when coexposed to both anions were similar for outer (292 ± 17 and 294 ± 12 L kg(-1) of dry weight, respectively) and inner (76 ± 18 and 60 ± 8 L kg(-1) of dry weight, respectively) leaves but not for roots (23 ± 3.7 and 359 ± 1.7 L kg(-1) of dry weight, respectively) when the iodine was supplied as I(-). The uptake of iodine was lower (BCF = 47 ± 3.8, 19 ± 0.6, and 189 ± 16, L kg(-1) of dry weight for the outer and inner leaves and roots, respectively) for all tissues when iodine was supplied as IO3(-), with the greatest accumulation by the roots. These results suggest that if lettuce is grown using fertilizers containing both ClO4(-) and I(-), then the final ratio of IT/ClO4 in the leaves will be essentially equal to the ratio in the fertilizer but lower if the I is supplied as IO3(-). Therefore, the impact of the consumption of lettuce containing ClO4(-) may be mitigated if the lettuce is grown using fertilizer with an appropriate amount of I to maintain the existing ratio of serum I to total goitrogen load (TGL). Nevertheless, the TGL in lettuce appeared to be almost completely dominated by NO3(-) with only a minor contribution of ClO4(-), even for the highest exposure to ClO4(-).