The Potential of Myrtaceae Species for the Phytomanagement of Treated Municipal Wastewater.

The use of native plants in land application systems for treated municipal wastewater (TMW) can contribute to ecological restoration. However, research on the potential of native species to manage the nutrients and contaminants contained in TMW is scarce. At a 10-hectare field site irrigated with TMW at >4000 mm yr-1, we investigated the distribution of nutrients and trace elements in the soil-plant system, comparing the New Zealand native Myrtaceae species Leptosperum scoparium and Kunzea robusta with pasture. The results showed that plant growth did not correlate with TMW irrigation rates. L. scoparium and K. robusta had higher foliar trace element concentrations than pasture, but these were not correlated with TMW irrigation rates. The pasture accumulated more N and P (68 kg of N ha-1 yr-1 and 11 kg of P ha-1 yr-1) than the Myrtaceae species (0.6-17 kg of N ha-1 yr-1 and 0.06-1.8 kg of P ha-1 yr-1). Regular harvesting of the pasture would likely remove more N and P from the site than the Myrtaceae species. The results highlight the importance of adjusting TMW application rates to the soil-plant capacity, in which case, native plants could provide ecological or economic value to TMW-irrigated land.

Investigation of triclosan contamination on microbial biomass and other soil health indicators.

Triclosan (TCS) is an antimicrobial compound found in personal care products, and consequently in greywater. After its release to the environment, it continues its antimicrobial action on indigenous microbial communities. Little is known about the environmental impacts of high levels of TCS, which may occur due to accumulation following long-term greywater application to soil. Soil microcosms were established using a silty clay loam and augmented with a range of TCS concentrations ranging from 500 to 7500 mg kg-1. Samples were analysed for substrate-induced respiration, microbial biomass and sulphatase activity. The soil augmented with the lowest concentration of TCS (500 mg kg-1) significantly decreased microbial biomass, with a calculated EC20 of 195 mg kg-1. Substrate-induced respiration indicated that the soil microbial community was impacted for all TCS concentrations; however, the community showed potential to recover over time. Sulphatase activity was less sensitive to TCS and was significantly impacted at high concentrations of TCS (>2500 mg kg-1). It is likely that TCS has selective toxicity for more susceptible microbes when introduced into the soil environment. At high levels, TCS could overwhelm TCS-degrading soil microbes.

Effects of long-term greywater disposal on soil: A case study.

This study investigated the environmental health risks to soil and potential risks to groundwater associated with long term (8-18years) greywater disposal practices. Land application of greywater is likely to have environmental impacts, which may be positive or negative. Greywater can contain plant macronutrients that may benefit plant growth. Conversely, high levels of surfactants, oils, grease, sodium and potentially pathogenic organisms may negatively impact environmental and human health. In this study, land disposal of untreated greywater was practiced at five coastal domestic properties. At each property, soil samples were collected at two depths from areas used for greywater disposal and from control areas that were not exposed to greywater. Soils were analysed for chemical and biological responses to greywater exposure. Generally, greywater irrigated soils had higher pH, Olsen P, base saturation, and increased soil microbial activity (as measured by biomass carbon, basal respiration and dehydrogenase activity). A pH of >9 was recorded for some greywater treated soil samples. Escherichia coli (E. coli) were detected at up to 10(3)MPN/g in the greywater exposed surface soils at some sites. Terminal Restriction Fragment Length Polymorphism (TRFLP) analysis revealed that greywater affected the soil microbial community structure, which may have implications for soil health and fertility. Overall, this study shows that the long-term application of greywater at the investigated sites had a moderate impact on the soil environment. This may have been due to the sandy soils and high rainfall that would flush the soil. Increases in microbial biomass and dehydrogenase indicate that greywater application may be beneficial for plant growth. However, high levels of E. coli in some soils may be a risk to human health and sub-surface irrigation should be the recommended application method.