title: Zinc solubility and fractionation in cultivated calcareous soils irrigated with wastewater.
abstract: The solubility, lability and fractionation of zinc in a range of calcareous soils from Peshawar, Pakistan were studied (18 topsoils and 18 subsoils). The lability (E-value) of Zn was assessed as the fraction isotopically exchangeable with (70)Zn(2+); comparative extractions included 0.005 M DTPA, 0.43 M HNO3 and a Tessier-style sequential extraction procedure (SEP). Because of the extremely low concentration of labile Zn the E-value was determined in soils suspended in 0.0001 M Na2-EDTA which provided reliable analytical conditions in which approximately 20% of the labile Zn was dissolved. On average, only 2.4% of soil Zn was isotopically exchangeable. This corresponded closely to Zn solubilised by extraction with 0.005 DTPA and by the carbonate extraction step (F1+F2) of the Tessier-style SEP. Crucially, although the majority of the soil CaCO3 was dissolved in F2 of the SEP, the DTPA dissolved only a very small proportion of the soil CaCO3. This suggests a superficial carbonate-bound form of labile Zn, accessible to extraction with DTPA and to isotopic exchange. Zinc solubility from soil suspended in 0.01 M Ca(NO3)2 (PCO2 controlled at 0.03) was measured over three days. Following solution speciation using WHAM(VII) two simple solubility models were parameterised: a pH dependent 'adsorption' model based on the labile (isotopically exchangeable) Zn distribution coefficient (Kd) and an apparent solubility product (Ks) for ZnCO3. The distribution coefficient showed no pH-dependence and the solubility model provided the best fit to the free ion activity (Zn(2+)) data, although the apparent value of log10 Ks (5.1) was 2.8 log units lower than that of the mineral smithsonite (ZnCO3).
authors.affiliation: Division of Agricultural and Environmental Sciences, School of Biosciences, University of Nottingham, Sutton Bonington, Leicestershire LE12 5RD, UK.
authors.forename: W
authors.initials: W
authors.lastname: Nazif
authors.affiliation: Division of Soil and Water Sciences, Faculty of Environmental Agricultural Sciences, Suez Canal University, North Sinai 45516, Egypt.
authors.forename: E R
authors.initials: ER
authors.lastname: Marzouk
authors.affiliation: Department of Soil and Environmental Sciences, Khyber Pakhtunkhwa Agricultural University, Peshawar, Pakistan.
authors.forename: S
authors.initials: S
authors.lastname: Perveen
authors.affiliation: Division of Agricultural and Environmental Sciences, School of Biosciences, University of Nottingham, Sutton Bonington, Leicestershire LE12 5RD, UK.
authors.forename: N M J
authors.initials: NM
authors.lastname: Crout
authors.affiliation: Division of Agricultural and Environmental Sciences, School of Biosciences, University of Nottingham, Sutton Bonington, Leicestershire LE12 5RD, UK. Electronic address: scott.young@nottingham.ac.uk.
authors.forename: S D
authors.initials: SD
authors.lastname: Young
mesh_terms: D057914:Agricultural Irrigation / Q000379:methods*; D002119:Calcium Carbonate / Q000737:chemistry; D004784:Environmental Monitoring; D010154:Pakistan; D012987:Soil / Q000737:chemistry; D012989:Soil Pollutants / Q000032:analysis / Q000737:chemistry*; D012995:Solubility; D014865:Waste Disposal, Fluid / Q000379:methods*; D062065:Wastewater / Q000737:chemistry*; D015032:Zinc / Q000032:analysis / Q000737:chemistry*
chemical_list: D002119:Calcium Carbonate; D012987:Soil; D012989:Soil Pollutants; D062065:Wastewater; D015032:Zinc
keywords: Calcareous soils; DTPA extraction; E-values; Metal solubility; Pakistan; Wastewater; Zinc