Effects of Garden Amendments on Soil Available Lead and Plant Uptake in a Contaminated Calcareous Soil

Abstract

Gardeners use organic and inorganic substances to enhance plant growth, which can inadvertently impact soil solubility and plant uptake of unknown contaminants. Consequently, human exposure can increase through gardening and consumption of produce grown in potentially contaminated soils. A greenhouse experiment was established to examine the effects of biochar, compost, and common inorganic fertilizer on soil lead (Pb) availability for radish (Raphanus sativus, L.) and lettuce (Lactuca sativa, L.) grown in a calcareous soil containing excessively high lead (Pb), along with Pb accumulation in radish tissue. Results indicate that soil amended with biochar and planted to radish saw an 18% reduction in available Pb and an 11% decrease in plant tissue content when compared to the control. Compost showed an 8% reduction in available Pb, but a 19% increase in tissue content. In contrast, soil with inorganic fertilizer planted to radish increased in both soil Pb availability by 11% and Pb tissue content by 40%. Adding water-soluble inorganic fertilizers to contaminated calcareous soils without added organic matter enhances soil Pb availability and often asymptomatic plant Pb bioaccumulation. In conclusion, gardeners are encouraged to test their soils for contamination and apply biochar in combination with compost, as this combination is recommended to improve soil health and aid in overcoming initial N deficiencies induced by biochar.

Trace Metal Contamination in Community Garden Soils across the United States

“…The disparity between lead concentrations within a small area highlights the need for thorough testing in community gardens and widespread remediation tactics. Applying a combination of compost and biochar can reduce the availability of lead, and applying a cover and using no-till agricultural practices will reduce lead mobilization [8,12,22,32]. However, the presence of dissolved organic carbon and other soil characteristics may affect the results, and this application may increase the bioaccessibility of arsenic.…”

“…Certain fertilizers that contain different plant nutrients can have the same effect on soil. For example, fertilizers containing ammonium decrease the negative charge of the soil, which increases lead availability, while fertilizers containing phosphates increase the negative charge and decrease lead availability [12,51]. Maintaining a neutral pH will ensure that the availability of all trace metals will stay low, which will decrease plant uptake [17].…”

“…High pH levels can facilitate the formation of metal carbonates and increase net negative charge, leading to the formation of metal-organic complexes [50]. Neutral-to-slightly basic pH will prevent the mobility of carbonate-bound metals [17], decrease the availability of cationic metals, such as lead, and increase the availability of anionic elements, such as arsenic [12]. A high soil pH can also reduce the leachability of cadmium zinc, immobilizing it in the soil [17].…”

“…Many of these contaminated sites in urban areas are a result of past industrialization. Cities also have many potential sources of trace metal contamination, such as old chipping lead paint, gasoline, runoff from nearby roads, fertilizer, municipal solid waste disposal, nearby mining, and nearby smelting [11][12][13][14][15]. The lack of consideration towards soil quality could lead to community members ingesting unhealthy levels of trace metals through inhalation or ingestion [16].…”

Estimation of Copper and Cadmium Bioavailability in Contaminated Soil Remediated by Different Plants and Micron Hydroxyapatite

“…Many methods have been used to evaluate the bioavailability of Cu and Cd, mainly including chemical extraction and some other methods such as the diffusive gradients in thin films (DGT). The dissolved part of heavy metals in soil is considered to have the highest bioavailability [ 17 ], 0.01 mol L −1 CaCl 2 often be used to extract the dissolved part metal fraction in soil [ 18 ]. As a kinetically based technique, DGT can reflect the soil metal desorption process when metals in the soil solution are depleted at the interface between the roots and the soil [ 19 ].…”