Lead and Arsenic Uptake by Leafy Vegetables Grown on Contaminated Soils: Effects of Mineral and Organic Amendments

Abstract

To assess strategies for mitigating Pb and As transfer into leafy vegetables from contaminated garden soils, we conducted greenhouse experiments using two field-contaminated soils amended with materials expected to reduce metal phytoavailability. Lettuce and mustard greens grown on these soils were analysed by ICP-MS, showing that some Pb and As transfer into the vegetables occurred from both soils tested, but plant Pb concentrations were highly variable among treatment replicates. Soil-to-plant transfer was more efficient for As than for Pb. Contamination of the leaves by soil particles probably accounted for most of the vegetable Pb, since plant Pb concentrations were correlated to plant tissue concentrations of the immobile soil elements Al and Fe. This correlation was not observed for vegetable As concentrations, evidence that most of the soil-to-plant transfer for this toxic metal occurred by root uptake and translocation into the above-ground tissues. A follow-up greenhouse experiment with lettuce on one of the two contaminated soils revealed a lower and less variable foliar Pb concentration than observed in the first experiment, with evidence of less soil particle contamination of the crop. This reduced transfer of Pb to the crop appeared to be a physical effect attributable to the greater biomass causing reduced overall exposure of the above-ground tissues to the soil surface. Attempts to reduce soil Pb and As solubility and plant uptake by amendment at practical rates with stabilizing materials including composts, peat, Ca phosphate, gypsum and Fe oxide, were generally unsuccessful. Only Fe oxide reduced soluble As in the soil, but this effect did not persist. Phosphate amendment rapidly increased soil As solubility but had no measurable effect on either soil Pb solubility or concentrations of Pb or As in the leafy vegetables. The ineffectiveness of these amendments in reducing Pb transfer into leafy vegetables is attributed in this study to the low initial Pb solubility of the studied soils and the fact that the primary mechanism of Pb transfer is physical contamination.

Urban home gardens in the Global North: A mixed methods study of ethnic and migrant home gardens in Chicago, IL

“…Research suggests that the uptake of soil lead by vegetable crops may be weak 23,24 . Inhalation or consumption of contaminated soil particles, though, represents another exposure pathway.…”

Concentrations of lead, cadmium and barium in urban garden-grown vegetables: The impact of soil variables

“…Highly variable physical contamination of vegetables (e.g., from dust, soil splash, traffic-related aerial contamination) related to local conditions, and the type of vegetable (with differing surface area and roughness of plants) (McBride et al, 2012; Nali et al, 2009; Säumel et al, 2012; Uzu et al, 2010). …”

“…Aluminum (Al) in the vegetables. Al is quite insoluble and unavailable for plant uptake at the near-neutral pH levels generally found in urban garden soils, and its presence in vegetable samples can be taken as an indicator of the physical presence of soil particles either in or on the washed vegetable samples (McBride et al, 2012). For example, washed vegetables were found to contain from 0.07 to 4.88% soil on a dry-weight basis (using immobile soil elements such as Al as indicators of vegetable contamination) (Cary et al, 1994).…”

Arsenic and Lead Uptake by Vegetable Crops Grown on an Old Orchard Site Amended with Compost

“…Arsenic uptake from orchard soils is frequently high enough to cause phytotoxicity in sensitive crops (Bishop and Chisholm 1962; Ross and Crowe 1976). Our own studies of As and Pb uptake from orchard soils by leafy green crops showed that there is a wide range of potential for uptake depending on crop species and the part of the plant analyzed (McBride 2013; McBride et al 2012). Thus, root and leafy crops have a much higher potential for Pb and As contamination than most vegetable fruits.…”