Andrew W. Rate

CADMIUM ACCUMULATION IN AGRICULTURAL SOILS IN WESTERN AUSTRALIA

Phosphatic fertilizers contain appreciable concentrations of cadmium (Cd) which may elevate the Cd concentrations of soils and crops, yet the impact of Cd on poorly buffered Western Australian soils is not known. We measured soil Cd, P and Zn concentrations at different depths and with total (mixed acid) and partial extractants (CaCl2, EDTA and HCl) at sites with a known phosphate fertilizer history. Accumulation of Cd in soils where P fertilizers had been applied varied greatly, with the Cd content of fertilized soils generally having significantly higher Cd contents than for unfertilized soils. In a ferruginous sandy loam, the highest concentrations of Cd were in the top 2 cm and these concentrations increased with increasing amounts of fertilizer application. A gravelly lateritic soil in an orchard contained 3.6 mg Cd kg-1, which was 20-fold higher than the equivalent unfertilized soil. Very sandy horticultural soils which are characteristic of Western Australia did not have higher exchangeable Cd, and showed small increases in total Cd, despite the high amounts of phosphatic fertilizers applied. The largest proportional increases in soil Cd were generally for analyses using partial extractants rather than for total Cd.

Adsorption of Au(I, III) complexes on Fe, Mn oxides and humic acid

The adsorption of AuCl4 � , AuCl2 � and Au(S2O3)2 3 � at low Au concentrations relevant to most supergene waters on geothite, birnessite and soil humic acid was investigated at pH 4, pH 2–11.6, in 0.01 and 0.1 M NaNO3 solutions. At pH 4 and two electrolyte strengths, the adsorption isotherms for the two Au chloride complexes are well described by the Freundlich equation. The Freundlich parameter 1/n reflects the heterogeneity of the birnessite surface and the nonlinearity of Au adsorption isotherm. The adsorption of Au(S2O3)2 3 � is significantly greater than that of AuCl4 � on birnessite, but the adsorption of Au(S2O3)2 3 � is significantly smaller for geothite and humic acid. The adsorption of AuCl4 � on birnessite and geothite is depressed by increasing electrolyte strength. As birnessite could only adsorb gold anions specifically and goethite could adsorb gold anions by anionic exchange and specific adsorption, the adsorption on goethite is more sensitive to the electrolyte strength. Under these experimental conditions, the Au surface coverage on birnessite is 0.68–0.85% for AuCl4 � and 1.06–1.10% for Au(S2O3)2 3 � , and for goethite is approximately 2.33–6.02% for AuCl4 � and 0.6–1.05% for Au(S2O3)2 3 � . For the pH ranges from 2 to 11.6 and with 0.1 M NaNO3 as the background electrolyte, Au adsorption decreases with increasing solution pH, which is consistent with the adsorption regularity for anion adsorption on a variable charge surface. For the three surfaces, true solid–liquid distribution coefficients for the Au complexes at these low concentrations that are relevant to most supergene water are significantly negatively correlated with solution pH with the correlation coefficient ranging from � 0.941 to � 0.996. According to the Kurbatov plot and surface hydroxyl density, the conditional equilibrium constants (log Kpart) can be estimated. For the three surfaces, values of log Kpart for adsorption of AuCl4 � are in the order: birnessite>goethite>humic acid; but for adsorption of AuCl2 � are goethite>birnessite>humic acid. The effect of the dissolved humic acid on data could be corrected by using a three-phase partition model that accounts for the complexation of the solute by dissolved organic matter in the liquid phase. For low pH (pH<3) solutions, the sorption of AuCl4 � on humic acid may be related to reduction of Au(III) by the humic acid. However, adsorption of AuCl4 � and AuCl2 � on humic acid is similar to that for birnessite and geothite for the higher pH solutions. Hence, birnessite, geothite, and humic acid preferentially adsorb chloro and chloro-hydroxo Au complexes produced from hydrolysis of AuCl4 � and AuCl2 � hydrolysis. Gold anion surface complexation and Au speciation in solution lead to the decrease in adsorption of Au complexes with increasing solution pH. As birnessite has very strong oxidation and adsorption abilities for monovalent Au complexes such as Au(S2O3)2 3 � , it may play an important role in the deposition and

Distribution of heavy metals in near-shore sediments of the Swan River estuary, Western Australia.

Estuarine systems adjacent to urban areas are at risk of contamination by contaminants from anthropogenic sources, such as heavy metals. We anticipated that the sediments of the Swan River estuary, which runs through metropolitan Perth in Western Australia, would show metal contamination related to industrialization and inputs of stormwater. Total Cu, Pb and Cd concentrations, and Cu, Pb, Cr and Zn inoperationally-defined fractions, were determined inseparate sampling exercises in near-shore sediments ofthe upper Swan River estuary.Total metal concentrations in sediments were not high (maximum values of 297 mg kg-1 for Cu, 184 mg kg-1 for Pb and 0.9 mg kg-1 for Cd) when compared with Australian environmental assessmentguidelines for soils. On the basis of linear regressions between sediment metal concentrations andphysicochemical properties of the sediments (pH, organic carbon, particle size distribution), no single parameter could explain the variation in metal concentrations for all metals. Sediment organic carbon content was positively correlated with Cu concentration; Cu concentrations also increased significantly with increasing clay content anddecreasing sand content. Pb concentrations showed a significant increase with increasing sediment pH, and were approximately three-fold higher in sediments adjacent to stormwater drain outfalls than in sediments remote from drains; no such effect was observed for Cu or Cd. No effect of distance downstream was observed. Sequential extraction of sediments showed that most of the metals were in relatively immobile forms, for example bound to Feoxides, or only extractable by aqua regia. The enhanced concentrations of Pb near stormwater outfalls suggest that vehicle-derived Pb may be an important contributor of Pb to the estuary.

Application of biosolids in mineral sands mine rehabilitation: use of stockpiled topsoil decreases trace element uptake by plants

Mineral sands mining involves stripping topsoil to access heavy-mineral bearing deposits, which are then rehabilitated to their original state, commonly pasture in south-west Western Australia. Organic amendments such as biosolids (digested sewage sludge) can contribute organic carbon to the rehabilitating system and improve soil chemical fertility and physical conditions. Use of biosolids also introduces the risk of contamination of the soil-plant system with heavy metals, but may be a useful source of trace elements to plants if the concentrations of these elements are low in unamended soil. We expected that biosolids amendment of areas mined for mineral sands would result in increased concentrations of metals in soils and plants, and that metal uptake would be decreased by adding stockpiled topsoil or by liming. A glasshouse experiment growing a mixed annual ryegrass (Lolium rigidum)-subterranean clover (Trifolium subterraneum) sward was conducted using two soil materials (residue sand/clay and conserved topsoil) from a mineral sands mine amended with different rates of biosolids (0, 10, 20, 50 dry t/ha), and including a liming treatment (2 t/ha). Total concentrations of metals (As, Cd, Co, Cr, Cu, Ni, Pb and Zn) in soil increased with increasing rate of biosolids application. Metal uptake was generally lower where topsoil was present and was decreased by liming. With increasing biosolids application, plant metal concentrations increased for Cd, Ni and Zn but decreased or were erratic for other elements. In clover, biosolids application removed the Zn deficiency observed where biosolids were not applied. Plant uptake of all elements increased with increasing biosolids application, suggesting dilution by increased plant biomass was responsible for erratic metal concentration results. Despite the observed increases in uptake of metals by plants, metal concentrations in both species were low and below food standard thresholds. It is unlikely that a single application of biosolids in this system posed a threat from heavy metal contamination of soils or plants, and was beneficial in terms of Zn nutrition of T. subterraneum.

Fate of nitrogen in pig slurry applied to a New Zealand pasture soil

A 2-year lysimeter study was conducted to determine the fate of nitrogen in pig slurry applied to a moderately fertile, semi-free-draining pasture soil in the Canterbury Plains of New Zealand. Pig slurry was applied annually for 2 years in autumn, at 3 rates of 0, 200, and 400 kg N/ha to 12 large soil lysimeters (4 at each rate), 800 mm in diameter by 1200 mm deep. Slurry applied in Year 1 was labelled with 15N and a mass balance obtained at the end of the experiment. The mass balance showed that over the 2 years following application of 15N-labelled slurry, 8–19% was lost in the leachate, 20% was removed in the cut pasture, 15–26% was lost via volatilisation, 14–18% remained in the roots and soil, and approximately 30% was lost by denitrification. The high denitrification loss was attributed to (i) a large soil concentration of nitrate supplied from nitrification of the ammonium-N in the slurry; (ii) a readily oxidisable source of carbon supplied in the slurry; and (iii) transient anaerobic conditions produced by textural discontinuities and impeding layers within the soil profile. The fate of applied nitrogen between years was affected by the pattern of water inputs (rainfall and irrigation) and the resulting effect on drainage. Concentrations of inorganic nitrogen in the leachate from the 200 kg N/ha·year treatment were found to be consistently below 25 mg N/L, but those from the 400 kg N/ha·year treatment were considerably higher (c. 65 mg N/L) and persisted for a prolonged period. The latter N concentration represented a significant loss of nitrogen over the study period and may be of environmental concern.

Water chemistry and nutrient release during the resuspension of FeS-rich sediments in a eutrophic estuarine system

The objective of this study was to investigate the impact of resuspending FeS-rich benthic sediment on estuarine water chemistry. To address this objective, we conducted (1) a series of laboratory-based sediment resuspension experiments and (2) also monitored changes in surface water composition during field-based sediment resuspension events that were caused by dredging activities in the Peel-Harvey Estuary, Western Australia. Our laboratory resuspension experiments showed that the resuspension of FeS-rich sediments rapidly deoxygenated estuarine water. In contrast, dredging activities in the field did not noticeably lower O(2) concentrations in adjacent surface water. Additionally, while FeS oxidation in the laboratory resuspensions caused measurable decreases in pH, the field pH was unaffected by the dredging event and dissolved trace metal concentrations remained very low throughout the monitoring period. Dissolved ammonium (NH(4)(+)) and inorganic phosphorus (PO(4)-P) were released into the water column during the resuspension of sediments in both the field and laboratory. Following its initial release, PO(4)-P was rapidly removed from solution in the laboratory-based (<1h) and field-based (<100 m from sediment disposal point) investigations. In comparison to PO(4)-P, NH(4)(+) release was observed to be more prolonged over the 2-week period of the laboratory resuspension experiments. However, our field-based observations revealed that elevated NH(4)(+) concentrations were localised to <100 m from the sediment disposal point. This study demonstrates that alongside the emphasis on acidification, deoxygenation and metal release during FeS resuspension, it is important to consider the possibility of nutrient release from disturbed sediments in eutrophic estuaries.

Fate of nitrogen in pig effluent applied to a shallow stony pasture soil

Abstract A 2‐year lysimeter experiment was conducted to determine the fate of nitrogen (N) in pig effluent applied to a shallow stony pasture soil. In the first year (1991), pig effluent was applied in a single application at three rates of total N (0, 200, and 600 kg N/ha) to 12 monolith lysimeters (500 mm diameter × 450 mm deep) during autumn (March). In the second year of the experiment, the 200 kg N/ha lysimeters received a repeat application using 15N‐labelled effluent. Application at the 200 kg N/ha rate resulted in: 10% of the applied N being lost by ammonia volatilisation; 5% being leached (11 kg N/ha) in the first year and less than 2.5% of applied 15N being leached in the second year; 35% of the applied effluent 15N was recovered by the pasture; and 14% was recovered in the soil plus roots. Denitrification losses (estimated by difference) were high (39%) and were attributed to the soluble carbon content of the effluent, a supply of nitrate from nitrification of slurry N, and transient anaerobic ...

Development of the diffusive gradients in thin films technique for the measurement of labile gold in natural waters.

Gold is a precious metal that exists in most soils, sediments, and natural waters at extremely low concentrations (<1 μg/kg). The diffusive gradients in thin films (DGT) technique, used extensively for measuring trace metal concentrations in soils, sediments, and waters, has potential for geochemical exploration for gold, but has not been developed for this metal. This work investigates the possibility of measuring labile gold using DGT by introducing a new binding layer based on activated carbon. The performance of this new technique was assessed using gold(III) chloride in solution by: (1) determining the diffusion coefficient of gold(III) in hydrogels; (2) determining the uptake of gold(III) chloride by the new activated carbon binding layer; (3) determining an elution methodology for the binding layer and evaluating its efficiency; (4) assessing the capacity of the activated carbon binding layer to adsorb gold; (5) determining the effect of pH and ionic strength (as NaCl) on performance, and (6) assessing the selectivity of the new binding layer for gold. It was found that the diffusion coefficient of gold(III) increased as solution pH decreased. The diffusion coefficient also increased at high ionic strength (≥0.1 M NaCl). Accounting for these phenomena, the DGT technique behaved predictably under all tested conditions. The technique can potentially be used as a geochemical exploration tool for gold in soils and in aqueous environments, with method detection limits as low as 0.9 ng/L for a 7-day deployment.

Trace element reactivity in FeS-rich estuarine sediments: Influence of formation environment and acid sulfate soil drainage

Iron monosulfides (FeS) precipitate during benthic mineralisation of organic C and are well known to have a strong influence on trace element bioavailability in sediments. In this study we investigate the reactivity of trace elements (As, Cd, Co, Cr, Cu, Mn, Mo, Ni, Pb, Zn) in sediments containing abundant and persistent FeS stores, collected from a south-western Australian estuarine system. Our objective was to explore the influence of sediment formation conditions on trace element reactivity by investigating sediments collected from different environments, including estuarine, riverine and acid sulfate soil influenced sites, within a single estuarine system. In general, we found a higher degree of reactivity (defined by 1 mol/L HCl extractions) for Cd, Mn, Pb and Zn, compared with a lower reactivity of As, Co, Cr, Cu, Mo and Ni. Moderate to strong correlations (R(2)>0.4, P<0.05) were observed between AVS and reactive Cd, Co, Mn, Mo, Ni, Pb and Zn within many of the formation environments. In contrast, correlations between AVS and As, Cr and Cu were generally poor (not significant, R(2)<0.4, P>0.05). Based on their reactivity and correlations with AVS, it appears that interactions (sorption, co-precipitation) between FeS and Cd, Mn, Pb and Zn in many of the sediments from this study are probable. Our data also demonstrate that drainage from acid sulfate soils (ASS) can be a source of trace elements at specific sites. A principal components analysis of our reactive (1 mol/L HCl extractable) trace element data clearly distinguished sites receiving ASS drainage from the other non-impacted sites, by a high contribution from Fe-Co-Mn-Ni along the first principal axis, and contributions from higher S-As/lower reactive Pb along the second axis. This demonstrates that trace element reactivity in sediments may provide a geochemical signature for sites receiving ASS drainage.

Wheat genotypes differ in growth and phosphorus uptake when supplied with different sources and rates of phosphorus banded or mixed in soil in pots

The growth response of wheat genotypes supplied with phosphorus fertiliser at different rates (banded or mixed throughout the soil) and sparingly soluble phosphorus sources (aluminium phosphate and iron phosphate) is not known. Eleven wheat genotypes and 1 rye genotype were tested at 3 rates of phosphorus fertiliser application (5, 10 and 20 mg P/kg soil) in a pot study. Another experiment compared 4 wheat genotypes at 2 rates of phosphorus application (deficient and sufficient) and 2 application methods (banding and mixing throughout the soil). The selected wheat genotypes were also used to investigate growth and root exudation response to iron phosphate and aluminium phosphate supply. Banding of phosphorus fertiliser increased the uptake of phosphorus and wheat growth compared with mixing phosphorus throughout the soil. Wheat genotypes did not differ significantly in growth and phosphorus uptake at the low rate of application. With increasing rates of phosphorus supply, the 2 phosphorus-fertiliser-responsive wheat genotypes (Wawht 2074 and Aroona) had significantly increased phosphorus uptake and root and shoot weights. When supplied with aluminium phosphate and iron phosphate, the 2 phosphorus-fertiliser-responsive genotypes had larger roots and higher concentration of phosphorus in the shoots and roots, while the phosphorus utilisation-efficient wheat genotypes (Westonia and Gutha) had higher shoot weights than phosphorus fertiliser-responsive ones. All wheat genotypes produced quantitatively and qualitatively similar root exudates in the iron phosphate, aluminium phosphate and zero-phosphorus treatments. The aluminium phosphate treatment caused genotypes to increase root exudation of oxalic anions, uptake of phosphorus and growth, compared with the iron phosphate treatment. It was concluded that the choice of genotypes for achieving increased wheat growth would depend on the phosphorus source in soil and the rate of application of phosphorus fertiliser.