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We conducted batch studies to investigate the effect of phosphate and dominant cations present in tannery waste on desorption of chromium (Cr) from surface and subsurface soil horizons from a contaminated tannery waste site at Mount Barker, South Australia. The surface horizon (0-15 cm) of the soil profile was alkaline (pH 7.9) and the subsurface horizon (50-90 cm) was acidic (pH 3.9). Aqua-regia extractable Cr concentration ranged from 62 g/kg in the surface to 0.26 g/kg in the subsurface soils. X-ray diffraction and scanning electron microscopic studies revealed the predominance of carbonate and kaolin minerals in the surface soils, and highly weathered framboidal particles, with morphology similar to that of pyrites, in the subsurface soils. The amount of Cr desorbed from the contaminated soils varied considerably with both the electrolyte's cationic charge and soil properties. The effect of cations, [Ca.sup.2+] and [Na.sup.+] (Ca[Cl.sub.2], NaCl), and phosphate on desorption of Cr was investigated. While the ionic strength of the solutions was standardised at approximately 0.03 mol/L, the concentration of phosphate (as [KH.sub.2][PO.sub.4]) was varied from 0 to 3.2 mmol/L. On the basis of studies on solution to soil ratio and desorption kinetics we chose a 20:1 solution to soil ratio and 2 h equilibration time. In the surface alkaline soil, the amount of Cr released decreased in the order [Na.sub.+] (286 µg/L) [is greater than or equal to] water (256 µg/L) [is greater than] [Ca.sup.2+] (156 µg/L). In contrast subsurface acidic soil showed a reverse trend, i.e. [Ca.sup.2+] (52 µg/L) [is greater than] [Na.sup.+] (29 µg/L) [is greater than] water (20 µg/ L). Speciation of Cr in the extracts showed predominantly Cr(VI) in the alkaline surface soil and Cr(III) in the subsurface acidic soil. A strong effect of phosphate on the cumulative amount of chromate desorbed was observed. The study shows that the presence of high concentrations of [Na.sup.+] (0.03 mol/L) and phosphate (3.2 mmol/L) in soil solution enhances Cr(VI) mobility. In contrast, [Ca.sup.2+] may induce retention of Cr(VI) in Cr-contaminated alkaline soils. Additional keywords: hexavalent chromium, chromate, leaching, contaminated site., Introduction Tanning industries worldwide generate approximately 40 million [m.sup.3] of waste containing chromium (Cr) every year (Macchi et al. 1991). With inadequate regulatory guidelines, wastes were largely disposed on land [...]

Abstract Sorption of 2 nonionic pesticides, carbaryl (1-naphthyl methylcarbamate) and phosalone (S-6-chloro-2,3-dihydro-2-oxobenzoxazol-3-ylmethyl O,O-diethyl phosphorodithioate), was investigated for 48 soils from Australia, Pakistan, and the United Kingdom. A wide variation in [...]

A field study was conducted on an alkaline cropping soil (plot size 4 m by 1 m), representative of cereal growing regions in southern Australia, to examine the degradation and leaching behaviour of triasulfuron, metsulfuron-methyl, and chlorsulfuron (150 g a.i./ha), along with a non-reactive tracer (KBr, 50 kg/ha), under 2 water treatments (`rainfall' and `rainfall + irrigation'). The results showed that the distributions of water content, [Br.sup.-] and the 3 herbicides were influenced by the amount of rainfall/irrigation received, and the biological activity as well as the physico-chemical properties of the soil within the profile. The largest concentrations of [Br.sup.-] were detected in the 10-20 cm depth under both treatments. No additional peak of [Br.sup.-] was observed in the plots which received only rainfall; however, there was another peak at 100 cm depth after a cumulative rainfall and irrigation of 158 mm. The spatial distribution of [Br.sup.-] in the plots was attributed to preferential flow through cracks or the presence of `mobile' and `immobile' water, which gave rise to bimodal distribution in the profile. Metsulfuron-methyl showed the greatest mobility, followed by chlorsulfuron and triasulfuron under both the treatments, with metsulfuron-methyl being detected at 120 cm depth under rainfall + irrigation. A bimodal distribution was also observed for the 3 herbicides, but the location of peaks was dependent on the solute. Rates of degradation of the herbicides could be described reasonably well with first-order reaction kinetics ([r.sup.2] = 0.72-0.91). The half-lives for triasulfuron, metsulfuron-methyl, and chlorsulfuron were 44, 45, and 32 days, respectively, under rainfall (69 mm), and 46, 59, and 48 days under rainfall + irrigation (158 mm). Additional keywords: sulfonylureas, dissipation, preferential flow, rainfall, irrigation., Introduction Triasulfuron, metsulfuron-methyl, and chlorsulfuron are the 3 most commonly used sulfonylurea herbicides for controlling broad-leaved weeds in the cereal crops of southern Australia. The compounds are weak acids (p[K.sub.a] [...]