Phosphate fertilizer additions to soils containing lead arsenate (LA) pesticide residues can increase As volubility. Apricot (Prunus armeniaca L.) rootstock liners were grown in nondraining pots containing Burch loam soil that received a factorial treatment combination: 1) LA enrichment [no added LA (-LA), and LA added at 138 mg Pb/kg and 50 mg As/kg (+LA)]; 2) fertilizer type [monoammonium phosphate (MAP) and its sulfur analog ammonium hydrogen sulfate (AHS)]; and 3) fertilizer anion rate (0-26.1 mol/m3 soil). Measured response variables were soil salinity and pH, plant biomass, and plant As and Pb concentrations. Both MAP and AHS increased soil electrical conductivity (EC) and decreased soil pH, with AHS usually being more salinizing and acidifying than MAP was at equivalent rates. Adding LA reduced shoot and root mass and increased As and Pb concentration in shoots and roots. Shoot and root mass were inversely related to soil EC in the -LA soil but not in the +LA soil. Adding MAP increased shoot and root As concentration in the +LA soil, but adding AHS had no effect. Fertilizer type and rate did not influence shoot As concentration or root Pb concentration in the -LA soil or shoot Pb concentration in either the +LA or -LA soil. Adding AHS to the +LA soil increased root Pb concentration. These results are consistent with a P-enhanced solid-phase As release mechanism, which consequently increases plant uptake of soil As. Phosphate amendment had no effect on soil Pb phytoavailability.
Concerns about food safety prompted a case study of the arsenic and Pb contents of tree fruits grown on lead arsenate-contaminated soil. The arsenic concentration in apricot (Prunus armeniaca L.) and `Gala' apple (Malus domestica Borkh.) fruit was positively related to concentrated HCl-extractable soil arsenic. Fruit arsenic in both species did not exceed 70 μg·kg-1 fresh weight (fw). Fruit Pb was below the limits of detection of 20 μg·kg-1 fw for apricot and 24 μg·kg-1 fw for apple. All of these concentrations are substantially below levels associated with human health risk. `Riland' apricot trees did not show arsenic phytotoxicity at soil, fruit, and leaf arsenic concentrations associated with phytotoxicity symptoms in `Goldrich' apricots. The apple trees showed no visual symptoms of arsenic phytotoxicity.
Fruit trees grown in soils contaminated with lead arsenate (PbHAsO4) pesticide residues are subject to arsenic (As) phytotoxicity, a condition that may be exacerbated by use of phosphate fertilizers. A potted soil experiment was conducted to examine the influence of phosphate fertilizer on accumulation of As and lead (Pb) in apricot (Prunus armeniaca) seedlings grown in a lead arsenate-contaminated Burch loam coil. Treatments were fertilizer source (mono-ammonium phosphate [MAP], ammonium hydrogen sulfate [AHS]) and rate (0, 8.7, 17.4, and 26.1 -mmol/liter), and presence/absence of lead, arsenate contamination (231 -mg/kg coil). Plant biomass accumulation was reduced by lead arsenate presence and by high fertilizer rates, the latter due to soil salinization. Phytoaccumulation of As was enhanced by lead arsenate presence and by increasing MAP rate but was not influenced by AHS rate, salinity, or acidity of soil. Phytoaccumulation of Pb was enhanced by lead arsenate presence but was not influenced by fertilizer treatment.
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