Australia is a large exporter of agricultural products, with producers responsible for a range of quality assurance programs to ensure that food crops are free from various contaminants of detriment to human health. Large volumes of treated sewage sludge (biosolids), although low by world standards, are increasingly being recycled to land, primarily to replace plant nutrients and to improve soil properties; they are used in agriculture, forestry, and composted. The Australian National Biosolids Research Program (NBRP) has linked researchers to a collective goal to investigate nutrients and benchmark safe concentrations of metals nationally using a common methodology, with various other research programs conducted in a number of states specific to regional problems and priorities. The use of biosolids in Australia is strictly regulated by state guidelines, some of which are under review following recent research outcomes. Communication and research between the water industry, regulators and researchers specific to the regulation of biosolids is further enhanced by the Australian and New Zealand Biosolids Partnership (ANZBP). This paper summarises the major issues and constraints related to biosolids use in Australia using specific case examples from Western Australia, a member of the Australian NBRP, and highlights several research projects conducted over the last decade to ensure that biosolids are used beneficially and safely in the environment. Attention is given to research relating to plant nutrient uptake, particularly nitrogen and phosphorus (including that of reduced phosphorus uptake in alum sludge-amended soil); the risk of heavy metal uptake by plants, specifically cadmium, copper and zinc; the risk of pathogen contamination in soil and grain products; change to soil pH (particularly following lime-amended biosolids); and the monitoring of faecal contamination by biosolids in waterbodies using DNA techniques. Examples of products that are currently produced in Western Australia from sewage sludge include mesophilic anaerobically digested and dewatered biosolids cake, lime-amended biosolids, alum sludge and compost.

Interest is mounting in developing and utilizing soil-specific soil quality guidelines. This requires quantifying the effects that soil physicochemical properties have on various ecotoxicological endpoints, including phytotoxicity. To this end, 14 agricultural soils from Australia with differing soil properties were spiked with copper (Cu) and zinc (Zn) salts and used to conduct 21-d plant growth inhibition tests using wheat (Triticum aestivum L.) in pot trials. The toxicity of Cu and Zn was similar with 10% effect concentration (EC10) values ranging from 110 to 945 and from 235 to 965 mg/kg, respectively, while the corresponding median effect concentration (EC50) values ranged from 240 to 1,405 and 470 to 1,745 mg/kg, respectively. Copper toxicity values (EC10, EC20, and EC50) were best modeled by the logarithm of cation exchange capacity (CEC) and either soil pH or electrical conductivity. Zinc EC50 and EC20 values were best modeled using the logarithm of CEC, while the EC10 data were best modeled using soil pH and the logarithm of organic carbon. These models generally estimated toxicity within a factor of two of the measured values.

To protect terrestrial ecosystems and humans from contaminants many countries and jurisdictions have developed soil quality guidelines (SQGs). This study proposes a new framework to derive SQGs and guidelines for amended soils and uses a case study based on phytotoxicity data of copper (Cu) and zinc (Zn) from field studies to illustrate how the framework could be applied. The proposed framework uses normalisation relationships to account for the effects of soil properties on toxicity data followed by a species sensitivity distribution (SSD) method to calculate a soil added contaminant limit (soil ACL) for a standard soil. The normalisation equations are then used to calculate soil ACLs for other soils. A soil amendment availability factor (SAAF) is then calculated as the toxicity and bioavailability of pure contaminants and contaminants in amendments can be different. The SAAF is used to modify soil ACLs to ACLs for amended soils. The framework was then used to calculate soil ACLs for copper (Cu) and zinc (Zn). For soils with pH of 4-8 and OC content of 1-6%, the ACLs range from 8 mg/kg to 970 mg/kg added Cu. The SAAF for Cu was pH dependant and varied from 1.44 at pH 4 to 2.15 at pH 8. For soils with pH of 4-8 and OC content of 1-6%, the ACLs for amended soils range from 11 mg/kg to 2080 mg/kg added Cu. For soils with pH of 4-8 and a CEC from 5-60, the ACLs for Zn ranged from 21 to 1470 mg/kg added Zn. A SAAF of one was used for Zn as it concentrations in plant tissue and soil to water partitioning showed no difference between biosolids and soluble Zn salt treatments, indicating that Zn from biosolids and Zn salts are equally bioavailable to plants.

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Alum sludge from wastewater treatment was applied at five rates on a phosphorus-deficient sand, and the effects on cereal growth and nutrition were investigated over 2 years. An inorganic fertilizer treatment, reapplied in the second year, was also included. The grain yield for inorganic fertilizer was 44% higher than the control in year 1 and 58% higher in year 2. Alum sludge was an adequate source of nitrogen for crop growth, and supplied sufficient residual nitrogen to meet crop requirements in year 2. However, grain yield in the alum sludge treatment applied at an equivalent available nitrogen rate to the inorganic fertilizer was 62% (year 1) and 69% (year 2) of the yield achieved by the inorganic fertilizer, though greater than the control. No toxic forms of aluminium were detected in the soil at any rate of alum sludge application. Plant shoot tissue analysis indicated that wheat sown in alum sludge-amended soil and the control were phosphorus deficient, whereas phosphorus was adequate in the inorganic fertilizer treatment. There was no evidence of any other nutrient deficiency. Alum sludge amendment resulted in an increase in soil phosphorus; however, further soil analysis indicated that forms of phosphorus present in alum sludge-amended soil may not be available for crop uptake; this is consistent with phosphorus deficiency observed in plant tissue in alum sludge-treated soil. It is suggested that on this nutrient-poor sand, the ability of alum sludge to provide sufficient phosphorus for plant production was limited in the 2 years after application.