Graham Merrington

The influence of sewage sludge properties on sludge-borne metal availability

With the advent of more stringent controls on wastewater treatment, sewage sludge production in Europe and many parts of the world is increasing. With this increase comes the problem of sludge disposal, and recycling to land arguably offers an economically and environmentally sustainable option. However, a major limitation of sewage sludge reuse is the potential release of heavy metals from the sludge and heavy metal accumulation to toxic levels in topsoils. The properties of the sludge play a crucial role in determining the initial release and subsequent availability of heavy metals in amended soils. Bioavailable forms of heavy metals in recently amended soils are most likely to be those that are bioavailable in the sewage sludge. In this paper, published research on the importance of sewage sludge characteristics on metal release and bioavailability will be reviewed and contrasted with original research. A selection of sludges from around Australia has been collected for this purpose. Through the use of incubation studies, isotope dilution techniques, ion-selective electrode measurements and 13C-NMR spectroscopy, the importance of a range of sludge properties on heavy metal behaviour in sludges and sludge-amended soils is addressed.

The potential impact of long-term copper fungicide usage on soil microbial biomass and microbial activity in an avocado orchard

The impact of copper-based fungicides on soil microbial function in an avocado orchard was assessed. Copper (Cu) residues (280 and 340 mg/kg, respectively) in surface soils (0-2 cm) of an established avocado orchard were shown to be significantly (n = 6, P ≤ 0.05) greater than a nearby reference site under natural vegetation (13 mg/kg). The bioavailable fraction of Cu in these soils was also shown to be significantly greater (2.15 and 1.29 mg/kg, c. pCu2+ 8.64) than in the reference site (0.71 mg/kg, c. pCu2+ 9.2), as measured by ion-selective electrode in CaCl2 extraction. Similar trends were observed for the 2-10 cm soil profile. Data suggest that the Cu residues are responsible for significant reductions in biomass carbon (Cmic) even though the orchard soils had similar or elevated levels of total organic carbon (Corg). The Cmic : Corg ratio was significantly lower in all of the Cu contaminated soils, and a significant correlation was observed between CaCl2-extractable Cu in the surface soils and Cmic (n = 16, r2 = 0.68, P b 0.01). Soil respiration in surface soils from the orchard were elevated (6.04 and 5.57 mg CO2-C/kg.day) compared with the reference soil (3.04 mg CO2-C/kg.day), and the metabolic quotient (qCO2) was also significantly greater.

Scientific derivation of environmental quality benchmarks for the protection of aquatic ecosystems: challenges and opportunities

In recent decades, the paradigm of water quality management has shifted from complete prohibition of pollutant discharge (i.e. zero tolerance) to permitting limited discharge of pollutants to receiving water bodies based on the results of a risk-based assessment approach. This approach assumes that the aquatic ecosystem is able to cope with certain levels of pollutants without harming aquatic life and the health of local communities who rely on the water body for food, drinking water and enjoyment. A risk-based approach also assumes that safe levels can be defined for pollutants that do not cause unacceptable disruptions of the structure and function of the aquatic ecosystem. This approach acknowledges the presence of uncertainty associated with the current understanding of substance-specific ecotoxicity, the behaviour of chemical mixtures in the environment, ecology of the receiving waters and the ability to measure chemical contaminants in effluents and receiving waters accurately. Furthermore, a risk-based approach acknowledges that the most serious water pollutants in terms of human health worldwide may not be man-made chemicals, but rather the pathogenic organisms originating from untreated or improperly treated human wastes. In developed countries, pollutioncontrol technologies have reduced or eliminated most of sources of pathogens in inland surface waters, thereby affording attention on other contaminants in water such as industrial chemicals, metals, and agricultural chemicals. The situation, however, is quite different in less-developed countries. In 2012, it was estimated that 37 % of the world’s population still lack adequate sanitation while 11 % of the global population could not gain access to clean drinking water (WHO 2012). From this perspective, the use of a riskbased approach that is able to focus attention on the largest water quality challenges and can confidently direct scarce financial resources to actions that will affect the largest results for protection of clean drinking water is of paramount importance. Scientists and environmental authorities are confronted with the realities facing less-developed countries, the nature of current scientific uncertainties and recognition that zero tolerance of water pollutants will likely have unacceptable economic consequences for societies striving to improve quality of life. It is self-evident, therefore, that the derivation of risk-based environmental quality guidelines, threshold values, limits, objectives and benchmarks by national regulatory authorities is gaining widespread acceptance as an appropriate foundation for national and international water quality management.

Copper and zinc water quality standards under the EU Water Framework Directive: the use of a tiered approach to estimate the levels of failure.

Environmental quality standards are an important tool for assessing the chemical quality of water bodies under the Water Framework Directive. However, there must be confidence in assessments of any failure to avoid disproportionate investment in unnecessary risk reduction. Metals present a number of unique challenges for environmental regulators in that they are naturally occurring and their ecotoxicology is driven, in part, by the physico-chemical conditions of the water body in which they are present. This paper describes the use of a tiered approach that could be adopted to assess compliance with any future environmental quality standards for metals under the Water Framework Directive. Through this approach, the use of background concentrations is considered and also bioavailability via the use of biotic ligand models. This assessment is based on an analysis of routine Environment Agency chemical monitoring data combined with biological indices to support results of the approach. Using copper and zinc as examples, it is shown that it is important to take account of background concentrations and the bioavailability of metals, otherwise the risk of impact from metals may be significantly overestimated. The approach presented here provides a methodology by which regulators and the regulated community may implement surface water standards for metals under the Water Framework Directive.

Transfer of cadmium and zinc from sewage sludge amended soil through a plant–aphid system to newly emerged adult ladybirds (Coccinella septempunctata)

An agricultural soil was amended with sewage sludge at rates equivalent to 0, 10 and 30 t (dry solids) ha−1 and the subsequent transfer of zinc and cadmium through a soil–plant–arthropod system was investigated. Zinc concentration in soil, wheat and aphids increased significantly with sludge amendment rate. Zinc was biomagnified during transfer along the pathway, resulting in concentrations in the aphids four times greater than in the soil. Cadmium concentration in the soil was also significantly elevated by the addition of sludge, but there was no significant difference in cadmium concentration in the shoots of wheat plants. Cadmium concentration in aphids followed the pattern found in plants, but again, differences between treatments were not significant. Aphids collected from the plants were subsequently fed to fourth instar Coccinella septempunctata. Consumption of these aphids did not result in significant differences between treatments in the body burden of newly emerged adult C. septempunctata for either metal. Sequestration of cadmium in the pupal exuviae had a greater effect on the body burden of newly emerged adult ladybirds than for zinc. Results are discussed in relation to possible risks posed by the transfer of trace metals via the soil–plant–arthropod system to predatory arthropods.

Development of biotic ligand models for chronic manganese toxicity to fish, invertebrates, and algae

Ecotoxicity tests were performed with fish, invertebrates, and algae to investigate the effect of water quality parameters on Mn toxicity. Models were developed to describe the effects of Mn as a function of water quality. Calcium (Ca) has a protective effect on Mn toxicity for both fish and invertebrates, and magnesium (Mg) also provides a protective effect for invertebrates. Protons have a protective effect on Mn toxicity to algae. The models derived are consistent with models of the toxicity of other metals to aquatic organisms in that divalent cations can act as competitors to Mn toxicity in fish and invertebrates, and protons act as competitors to Mn toxicity in algae. The selected models are able to predict Mn toxicity to the test organisms to within a factor of 2 in most cases. Under low-pH conditions invertebrates are the most sensitive taxa, and under high-pH conditions algae are most sensitive. The point at which algae become more sensitive than invertebrates depends on the Ca concentration and occurs at higher pH when Ca concentrations are low, because of the sensitivity of invertebrates under these conditions. Dissolved organic carbon concentrations have very little effect on the toxicity of Mn to aquatic organisms.

The tri-trophic transfer of Zn from the agricultural use of sewage sludge

Abstract An agricultural soil in Southern England was amended with two annual applications of sewage sludge at rates of 0, 10 and 15 t ha −1 dry solids. Soil concentrations of Zn reached 31.1 μg g −1 and the subsequent uptake was measured in wheat plants ( Triticum aestivum ), grain aphids ( Sitobion avenae ) and a predatory carabid beetle ( Bembidion lampros ) in order to test the hypothesis that Zn was transferred through this tri-trophic food chain. Concentrations of Zn in the wheat plants, aphids and predatory beetles reached 31.7, 116.0 and 242.2 μg g −1 dry wt., respectively. A potential exposure pathway from soil→plant→herbivore→predator was identified, the concentration of Zn in the predatory beetle being related to the amount of aphids eaten and sewage sludge application rate. The concentrations of Zn in the sludge-amended soils were all well within current UK regulation limits and the relevance of exposure pathways at sub-critical concentrations when considering metal loading rates for sewage sludge amended soils is discussed.

Cadmium sorption in biosolids amended soils: results from a field trial

The effect of biosolids amendment on cadmium sorption coefficient (K(d)) was determined for soils in a biosolids field trial. The sorptive properties of biosolids are thought to have a significant controlling effect upon the availability/uptake and mobility of potentially toxic metals. K(d) values for the three biosolids were 10-30 times greater than those for unamended soil. Elevated K(d) values were still apparent 1 and 2 years after biosolids amendment (100 t ha(-1)) for two of the three biosolids. Chemical extractants (sodium hypochlorite and hydrofluoric acid, respectively) were used in an attempt to determine K(d) values of isolated inorganic and organic fractions. For both biosolids amended soils and unamended controls, Cd sorption appeared to be dominated by the inorganic fraction, potentially indicating the overriding importance of this fraction in controlling metal mobility. However, for the biosolids themselves, the sum of inorganic and organic fraction contributions to K(d) accounted for less than half the K(d) of the whole biosolids. This discrepancy was attributed to the loss of highly sorptive water soluble species in both chemical extractions.

Water quality guidelines for chemicals: learning lessons to deliver meaningful environmental metrics

Many jurisdictions around the globe have well-developed regulatory frameworks for the derivation and implementation of water quality guidelines (WQGs) or their equivalent (e.g. environmental quality standards, criteria, objectives or limits). However, a great many more still do not have such frameworks and are looking to introduce practical methods to manage chemical exposures in aquatic ecosystems. There is a potential opportunity for learning and sharing of data and information between experts from different jurisdictions in order to deliver efficient and effective methods to manage potential aquatic risks, including the considerable reduction in the need for aquatic toxicity testing and the rapid identification of common challenges. This paper reports the outputs of an international workshop with representatives from 14 countries held in Hong Kong in December 2011. The aim of the workshop and this paper was to identify ‘good practice’ in the development of WQGs to deliver to a range of environmental management goals. However, it is important to broaden this consideration to cover often overlooked facets of implementable WQGs, such as demonstrable field validation (i.e. does the WQG protect what it is supposed to?), fit for purpose of monitoring frameworks (often an on-going cost) and finally how are these monitoring data used to support management decisions in a manner that is transparent and understandable to stakeholders. It is clear that regulators and the regulated community have numerous pressures and constraints on their resources. Therefore, the final section of this paper addresses potential areas of collaboration and harmonisation. Such approaches could deliver a consistent foundation from which to assess potential chemical aquatic risks, including, for example, the adoption of bioavailability-based approaches for metals, whilst reducing administrative and technical burdens in jurisdictions.

Australian Biosolids: Characterization and Determination of Available Copper

Environmental Context. Land application of sewage-derived biosolids is both an inexpensive method to dispose of waste and a simple way to increase soil fertility and stability. However, biosolids often contain high concentrations of heavy metals, but not all of the metals are immediately available for uptake by the soil or other organisms. To determine if this toxicologic risk outweighs the benefits, the degree of ecologically available metal, rather than simply the entire metal content, must be known in both the as-disposed and worst conditions scenarios. Application of these principles requires regulatory bodies to amend their guidelines. Abstract. Application of biosolids to agricultural land provides a low-cost disposal option with many potential benefits to soil. However, the practice may result in accumulations of potentially toxic heavy metals, and thus regulations are in place to limit the amount of metals applied to soil in this way. Current Australian regulations are not ideal because they are based on total metal concentrations in soils and biosolids, rather than the fraction that is ecologically available (the fraction accessible by organisms). Therefore more environmentally appropriate regulations, based on the available metal portion, need to be devised. However, before this is possible, more needs to be known about the characteristics of Australian biosolids, including the factors that influence the availability of biosolid metals. Copper is a metal of great concern because of its commonly high concentration in biosolids and because of its relatively high toxicity to certain groups of bacteria and fungi. Therefore an investigation was conducted to characterize the range of properties observed in Australian biosolids, and to determine the fraction of available metals and the factors that influence it (particularly in the case of copper). General properties such as pH, electrical conductivity, organic carbon, and total metal concentrations were measured. Availability of copper was specifically measured using isotopic exchange techniques and a Cu2+ ion-selective electrode. Results showed that total copper concentration and Cu2+ activity could be used to predict available copper. A new system of biosolid land-use regulation that incorporates the available metal fraction and a pH protection factor is proposed.