Environmental Sciences

Polluted and contaminated soils can often contain more than one heavy metal species. It is possible that the behavior of a particular metal species in a soil system will be affected by the presence of other metals. In this study we have investigated the adsorption of Cd(II), Cu(II), Pb(II), and Zn(II) onto kaolinite in single- and multi-element systems as a function of pH and concentration, in a background solution of 0.01 M NaNO3. In adsorption edge experiments, the pH was varied from 3.5 to 10.0 with total metal concentration 133.3 microM in the single-element system and 33.3 microM each of Cd(II), Cu(II), Pb(II), and Zn(II) in the multi-element system. The value of pH50 (the pH at which 50% adsorption occurs) was found to follow the sequence Cu<Zn<Pb<Cd in single-element systems, but Pb<Cu<Zn<Cd in the multi-element system. Adsorption isotherms at pH 6.0 in the multi-element systems showed that there is competition among various metals for adsorption sites on kaolinite. The adsorption and potentiometric titrations data for various kaolinite-metal systems were modeled using an extended constant-capacitance surface complexation model that assumed an ion-exchange process below pH 7.0 and the formation of inner-sphere surface complexes at higher pH. Inner-sphere complexation was more dominant for the Cu(II) and Pb(II) systems.

Dietary exposure to heavy metals, namely cadmium (Cd), lead (Pb), zinc (Zn) and copper (Cu), has been identified as a risk to human health through the consumption of vegetable crops. This study investigates the source and magnitude of heavy metal contamination in soil and vegetable samples at 46 sites across four vegetable growing regions in New South Wales, Australia. The four regions Boolaroo, Port Kembla, Cowra and the Sydney Basin were a mix of commercial and residential vegetable growing areas. The extent of metal contamination in soils sampled was greatest in regions located in the vicinity of smelters, such as in Boolaroo and Port Kembla. Soil metal concentrations decreased with depth at these two sites, suggesting contamination due to anthropogenic activities. Cadmium, Pb and Zn contamination was greatest in vegetables from Boolaroo, and Cu concentrations were greatest in vegetables sampled from Port Kembla. At Boolaroo, nearly all the samples exceeded the Australian Food Standards maximum level (ML) (0.01 mg kg−1 fresh weight) of Cd and Pb in vegetables. Over 63% of samples exceeded international food standard guidelines set by the Commission of the European Communities and the Codex Alimentarius Commission. All vegetables sampled from Cowra, which is a relatively pristine site had Cd and Pb levels below the Australian and international food standards guideline values. This study suggests that the Australian guideline values are more conservative in defining the ML for Cd and Pb in vegetable crops. This investigation highlights the increased danger of growing vegetables in the vicinity of smelters.

ABSTRACT The mechanisms responsible for nickel (Ni) hyperaccumulation in Hybanthus floribundus (Lindl.) F. Muell. subspecies floribundus are obscure. In this study, organic acids and free amino acids (AAs) were quantified in 0.025 M HCl H. floribundus subsp. floribundus shoot extracts using HPLC and ultra performance liquid chromatography (UPLC). In a 20 week pot experiment, plants exposed to five levels of Ni (0-3000 mg kg(-1) Ni) accumulated up to 3200 mg Ni kg(-1) dry weight in shoots, and the shoot : root Ni concentration ratios were >1.4. Concentration of organic acids followed the order malic acid >citric acid > oxalic acid. Citric acid concentration significantly increased upon Ni exposure, with concentrations between 2.3- and 5.9-fold higher in Ni treated plants that in control plants. Molar ratios of Ni to citric acid ranged from 1.3 : 1 to 1.7 : 1 equivalent to >60% of the accumulated Ni. Malic acid concentration also increased upon exposure to applied Ni. However, concentrations were statistically at par across 0-3000 mg kg(-1) Ni treatments, suggesting that the production of malic acid is a constitutive property of the subspecies. Total AA concentrations were stimulated upon exposure to external Ni treatment, with glutamine, alanine and aspartic acids being the predominant acids. These AAs accounted for up to 64% of the total free AA concentration in control plants and up to 75% for the 2000 mg kg(-1) Ni treatment plants. These results suggest that citric acid in addition to the aforementioned AAs are synthesised in H. floribundus subsp. floribundus plants following exposure to elevated concentrations of Ni and may act as potential ligands for detoxification and possibly storage of accumulated Ni.

ABSTRACT Intensive greenhouse industry wastes large amounts of nutrient-rich green waste through improper disposal practices. Converting this greenhouse waste into biochar for soil application offers a viable option to recycle nutrients and long-term C storage. This study was carried out to evaluate the agronomic potential of a biochar produced from tomato green waste in two contrasting soils. We also estimated the amount of waste generated from intensive greenhouse tomato production in Australia. From weekly measurements of leaf picking over a 13-week period, we estimate approximately 133 Mg ha−1 year−1 of green waste on fresh weight basis. Biochar, produced by slowly pyrolysing the green waste at 550 °C, had very high-pH (12.1), electrical conductivity (EC, 54.2 dS m−1), ash content (560 g kg−1) and CaCO3 equivalence (330 g kg−1). Agronomic performance of the biochar was evaluated by growing Hybrid sweet corn (Zea mays var. rugosa cv – Sentinel) in the greenhouse for 7 weeks. We used three levels of biochar (0, 5 and 15 g kg−1 soil) in a factorial combination with three fertiliser rates (0, 50 and 100% of the recommended rate) applied to two contrasting soils (an Orthic Tenosol and a Red Ferrosol). Biochar application to the Ferrosol significantly increased the shoot dry matter of corn and contrastingly decreased the yield in case of the Tenosol. The positive effect of the biochar in the Ferrosol was attributed to release of nutrients from the biochar and biochar's liming effect and associated increased availability of nutrients. However, in poorly buffered Tenosol the application of biochar produced phytotoxic effects due to excessive soluble salts and high pH. The uptake of most nutrient elements increased in the corn shoot in the Ferrosol and decreased in the Tenosol. Although the biochar produced from green waste was highly alkaline and contained excessive soluble salts, given the right soil properties it can be a good soil ameliorant. The true agronomic potential of the biochar should be further evaluated in different soil types under field conditions.