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In situ stabilization of Pb contaminated soils can be accomplished by adding P and Mn(IV) oxide. However, the long-term efficacy of in situ stabilization under continual P removal through plant growth is unknown. Moreover, the effects these treatments have on phytoavailability of other metals (Cd and Zn) commonly associated with Pb in soil are not well understood. Greenhouse experiments using sudax [Sorghum vulgare (L.) Moench] and Swiss chard [Beta vulgaris (L.) Koch] were carried out to evaluate the effects of plant growth on soil Pb bioavailability to humans after addition of P and other amendments, and the effects of these treatments on Pb, Cd, and Zn phytoavailability in three metal-contaminated soils. Eight treatments were used: zero P; 2500 mg of P as triple superphosphate (TSP); 5000 mg of P as TSP or phosphate rock (PR); 5000 mg of Mn oxide/kg; and combinations of Mn oxide and P as TSP or PR. The addition of P and/or Mn oxide significantly reduced bioavailable Pb, as measured by the physiologically based extraction test (PBET), in soils compared with the control even after extensive cropping. The PBET data also suggested that removal of P from soluble P sources by plants could negate the beneficial effects of P on bioavailable Pb, unless sufficient soluble P was added or soluble P was combined with Mn oxide. In general, Ph, Cd, and Zn concentrations in shoot tissues of sudax and Swiss chard were reduced significantly by TSP and did not change with the addition of PR. The combination of PR and Mn oxide significantly reduced Pb concentrations in plants compared with the control.

The environmental risk from soil lead (Pb) is related to its bioavailability. Soil Pb bioavailability depends on the solubility of Pb solid phases and other site‐specific soil chemistry, suggesting that in situ stabilization of soil Pb can be accomplished by changing soil Pb chemistry. This paper presents a review of soil Pb bioavailability and an evaluation of in situ stabilization methods that can be used to reduce Pb bioavailability. A promising in situ approach involves the amendment of Pb‐contaminated soil with phosphorus (P) in various forms or P with other amendments. Two general categories of P are insoluble forms, such as phosphate rock or synthetic apatites, and soluble forms typically present in commercially available fertilizer products or phosphoric acid. Numerous indirect assessment techniques show marked reductions in soil Pb biovailability upon addition of P and other amendments to Pb‐contaminated soils. The techniques include physiologically based extraction tests, plant uptake of Pb, and other soil Pb extraction methods. More directly, animal feeding studies also show reductions in soil Pb biovailability. In situ stabilization of soil Pb using P and other soil amendments is an emerging technology integrating soil chemistry, agricultural practices, and engineering that is gaining public and regulatory acceptance. © 2004 American Institute of Chemical Engineers Environ Prog, 23: 78–93, 2004

In situ stabilization of Pb-contaminated soils can be accomplished by adding phosphorus. The standard remediation procedure of soil removal and replacement currently used in residential areas is costly and disruptive. This study was carried out to evaluate the influence of P and other soil amendments on five metal-contaminated soils and mine wastes. Seven treatments were used: unamended control; 2,500 mg of P/kg as triple superphosphate (TSP), phosphate rock (PR), acetic acid followed by TSP, and phosphoric acid (PA); and 5,000 mg of P/kg as TSP or PR. A significant reduction in bioavailable Pb, as determined by the physiologically based extraction test (PBET), compared with the control upon addition of P was observed in all materials tested. Increasing the amount of P added from 2,500 to 5,000 mg/kg also resulted in a significantly greater reduction in bioavailable Pb. Phosphate rock was equally or more effective than TSP or PA in reducing bioavailable Pb in four out of five soils tested. Preacidification produced significantly lower bioavailable Pb compared with the same amount of P from TSP or PR in only one material. Reductions in Pb bioavailability as measured by PBET were evident 3 d after treatment, and it may indicate that the reactions between soil Pb and P occurred in situ or during the PBET. No further reductions were noted over 365 d. X-ray diffraction data suggested the formation of pyromorphite-like minerals induced by P additions. This study suggests that P addition reduced bioavailable Pb by PBET and has potential for in situ remediation of Pb-contaminated soils.

Lead (Pb) is one of the most common contaminants in urban soils. Gardening in contaminated soils can result in Pb transfer from soil to humans through vegetable consumption and unintentional direct soil ingestion. A field experiment was conducted in 2009 and 2010 in a community urban garden with a soil total Pb concentration of 60 to 300 mg kg−1. The objectives of this study were to evaluate soil–plant transfer of Pb, the effects of incorporation of a leaf compost as a means of reducing Pb concentrations in vegetables and the bioaccessibility of soil Pb, and the effects of vegetable cleaning techniques on the Pb concentrations in the edible portions of vegetables. The amount of compost added was 28 kg m−2. The tested plants were Swiss chard, tomato, sweet potato, and carrots. The vegetable cleaning techniques were kitchen cleaning, laboratory cleaning, and peeling. Compost addition diluted soil total Pb concentration by 29 to 52%. Lead concentrations of the edible portions of vegetables, except carrot, were below the maximum allowable limits of Pb established by the Food and Agriculture Organization and the World Health Organization. Swiss chard and tomatoes subjected to kitchen cleaning had higher Pb concentrations than laboratory‐cleaned plants. Cleaning methods did not affect Pb concentrations in carrots. Bioaccessible Pb in the compost‐added soils was 20 to 30% less than that of the no‐compost soils; compost addition reduced the potential of transferring soil Pb to humans via vegetable consumption and direct soil ingestion. Thorough cleaning of vegetables further reduced the potential of transferring soil Pb to humans.

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Soil fertility provides the foundation for nutritious food production and resilient and sustainable livelihoods. A comprehensive survey and summit meeting were conducted with the aims of understanding barriers to enhancing soil fertility in sub-Saharan Africa and providing evidence-based recommendations. The focus regions were West Africa, East Africa, the Great Lakes region, and Ethiopia. Overall recommendations were developed with four emerging themes: (1) strengthening inorganic fertilizer-based systems, (2) access to and use of quality organic inputs, (3) capacity building along the entire knowledge-transfer value chain, and (4) strengthening farming systems research and development across biophysical and socio-economic factors. The evidence-based process and methodology for prioritizing these recommendations makes these findings useful for setting out action plans for future investments and strategies. Access to inorganic fertilizer, its use, and related implementation issues were prominent considerations; nevertheless, biophysical and socio-economic barriers and solutions were identified as equally important to building soil fertility and natural resources. Soil management initiatives should focus on providing holistic solutions covering both biophysical and socio-economic aspects along the entire value chain of actors and creating an enabling environment for adoption. A broader view of soil fertility improvement using all available options including both inorganic and organic sources of nutrients and farming system approaches are highly recommended.