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Risks Associated with Application of Municipal Biosolids to Agricultural Lands in a Canadian Context By Dr. Jorge E. Loyo-Rosales and Dr. Lynda H. McCarthy, Ryerson University The Canadian Water Network (CWN) commissioned a review of the current knowledge on the occurrence, fate, and potential risks of emerging substances of concern (ESOCs) and pathogens present in biosolids after application to agricultural land, especially in conditions relevant to Canada. The review will serve as the basis for a national consultation to be conducted by CWN’s Canadian Municipal Water Consortium on this topic in the context of the sustainability of biosolids land application. ESOCs and pathogens are the main focus of the review because existing regulations do not explicitly address these newly identified chemicals and pathogens. Recent advances in analytical chemistry have allowed the detection in biosolids of a large number of substances (ESOCs), some of them present in low concentrations, but whose potential impact to public and environmental health is not yet determined. Similarly, the development of new detection and identification methods has led to the recognition of additional pathogens in biosolids. In addition, changes in water treatment technologies, and the introduction of new pathogenic organisms, either from distant geographical locations or through evolution of the microorganisms themselves, could also play a significant role in the emergence of pathogens in biosolids. The review covers a wide variety of topics related to ESOCs and pathogens in biosolids-amended soils. Topics covered include: risk assessment, the effects of sludge treatment on concentration and viability of ESOCs and pathogens, their fate in soils after biosolids application, biological impact studies, and public acceptance of biosolids land application. This article summarizes some of the general findings of the review. Risk assessments: Few risk assessments have been conducted for ESOCs in the biosolids land application context, and they suggest that ESOCs pose a low risk to human and environmental health. More risk assessments have been conducted for pathogens, and their risk is considered low or practically nonexistent for the general population. Pathogens are only considered an issue in worst-case occupational scenarios, such as biosolids applicators with no protective equipment. Sludge treatment: The review notes that sludge treatment generally results in a net reduction of ESOCs mass and effects (e.g., estrogenicity), and in the number of pathogenic organisms. However, the magnitude of the reduction depends on factors such as the nature of the specific compounds or organisms, and the type and conditions of treatment. For example, ESOCs such as carbamazepine, and pathogens such as enteroviruses are resistant to some or most treatment methods. Environmental fate: The fate of biosolids-related ESOCs and pathogens after land application is a complex, site-specific phenomenon driven by the combination of a large number of factors, ranging from the properties of the ESOCs or pathogens and the soils, to environmental variables such as temperature and soil moisture content, and the biosolids application methods. Therefore, the ultimate fate of individual ESOCs and pathogens is very variable, with some (e.g., triclosan, Cryptosporidium) persisting in the soil for long periods of time, while others are very mobile (e.g., iopromide) or degradable. However, studies generally conclude that most of the compounds typically found in biosolids do not reach the groundwater after land application, and that their concentrations in tile drainage and surface runoff tend to be much lower than typical concentrations found in WWTP effluents. ESOCs uptake by plants and bioaccumulation by earthworms: Both phenomena have been clearly demonstrated, although they might have been overestimated by the use of proof-of-concept methodologies that do not reflect relevant environmental and agricultural conditions. In addition, accumulation of ESOCs in soil, crops, or soil organisms might not be desirable, but their sole presence does not constitute proof of negative impact. Antibiotic resistance: The presence of antibiotic resistant bacteria (ARB) in sludge and biosolids is well documented, but incidence tends to be lower than in other environmental compartments. The risk of antibiotic-resistance gene transfer in soil is considered to be low, and land-applied biosolids are not expected to affect the incidence of antibiotic resistance in pathogens. 56 INFLUENTS Fall 2015 Click HERE to return to Table of contents
Impact on biota: Soil amendment with biosolids at agronomic rates has a positive impact on plants. Studies on invertebrates (e.g., earthworms) show mixed results, with negative impact being associated with high heavy metal concentrations, ammonia, pH or salinity levels. Microbial biomass and activity increase, except when high metal concentrations are present, but the ecological significance of these effects has not been elucidated. Use of omics and biomarkers: Although ‘omics’ technologies have the potential to improve the study of toxicity effects resulting from simultaneous exposure to multiple chemicals, the development of antibiotic resistance, and ecosystem health assessment, their use in the biosolids field is still in its infancy. The use of biomarkers, such as estrogenicity, can provide valuable information on the possible effects of biosolids to biota without the need for exhaustive chemical analysis. However, research is still necessary to relate the responses of biomarker tests to actual impact on individuals and populations. The overall conclusion of the review is that a different strategy is necessary to determine whether ESOCs in the biosolids land-application context affect human and/or environmental health. This new strategy should be based on the evaluation of ecosystem health, and it should take into account ESOCs in other contexts to provide a more holistic perspective. For example, if a chemical is banned or its use restricted, its concentrations in biosolids will eventually decrease and investment in additional treatment to eliminate such chemical might be unnecessary. From a public health perspective, conducting scientifically-based inquiries following reports of adverse health effects, especially by residents neighbouring biosolids-amended fields, would be a significant contribution to elucidate the possible links of these health effects to biosolids exposure. Finally, the strategy should be designed considering other factors affecting the sustainability of biosolids land application, such as energy demand and greenhouse gas emissions. This is especially important when comparing land application to other beneficial uses for biosolids, such as gas co-generation and recovery from anaerobic digestion, and power generation from incineration in wasteto-energy (WtE) systems. Click HERE to return to Table of contents INFLUENTS Fall 2015 57
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