Natural perchlorate (ClO4 −) in soil and groundwater exhibits a wide range in stable isotopic compositions (δ37Cl, δ18O, and Δ17O), indicating that ClO4 − may be formed through more than one pathway and/or undergoes post-depositional isotopic alteration. Plants are known to accumulate ClO4 −, but little is known about their ability to alter its isotopic composition. We examined the potential for plants to alter the isotopic composition of ClO4 − in hydroponic and field experiments conducted with snap beans (Phaseolus vulgaris L.). In hydroponic studies, anion ratios indicated that ClO4 − was transported from solutions into plants similarly to NO3 − but preferentially to Cl− (4-fold). The ClO4 − isotopic compositions of initial ClO4 − reagents, final growth solutions, and aqueous extracts from plant tissues were essentially indistinguishable, indicating no significant isotope effects during ClO4 − uptake or accumulation. The ClO4 − isotopic composition of field-grown snap beans was also consistent with that of ClO4 − in varying proportions from irrigation water and precipitation. NO3 − uptake had little or no effect on NO3 − isotopic compositions in hydroponic solutions. However, a large fractionation effect with an apparent ε (15N/18O) ratio of 1.05 was observed between NO3 − in hydroponic solutions and leaf extracts, consistent with partial NO3 − reduction during assimilation within plant tissue. We also explored the feasibility of evaluating sources of ClO4 − in commercial produce, as illustrated by spinach, for which the ClO4 − isotopic composition was similar to that of indigenous natural ClO4 −. Our results indicate that some types of plants can accumulate and (presumably) release ClO4 − to soil and groundwater without altering its isotopic characteristics. Concentrations and isotopic compositions of ClO4 − and NO3 − in plants may be useful for determining sources of fertilizers and sources of ClO4 − in their growth environments and consequently in food supplies.
- Chlorine isotopes
- Isotope fractionation in snap beans (Phaseolus vulgaris L.)
- Nitrogen isotopes
- Oxygen isotopes
- Plant uptake