Potentially hazardous agents in land-applied sewage sludge: human health risk assessment
This report on the risks to human health is part of the research project undertaken by the James Hutton Institute on the impacts on human health and environment arising from the spreading of sewage sludge to land (CR/2016/23).
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4. Conclusions
Under good practice (e.g. adherence to the Safe Sludge Matrix) and normal circumstances, none of the potentially hazardous agents assessed posed significant health risks. Under realistic worst-case circumstances, a number of potentially hazardous agents were estimated to pose risk to health for human receptors. These are listed in Table 4‑1 along with possible mitigation suggestions. It should be noted that these potential risks have been identified as part of a theoretical mathematical exercise with any mitigation (e.g. by taking a precautionary approach to minimise or eliminate potential risks) only necessary if the predicted exposures and associated risks were found to be real.
| Potentially hazardous agent | Outome | Magnitude of risk (worst case) | Uncertainty | Possible mitigation |
|---|---|---|---|---|
| Malodour | Annoyance | Medium | High |
|
| Nonylphenol | HQ>1 | Low | Medium |
|
| Nonylphenol diethoxylate | HQ>1 | Low | High | |
| PBDE-99 | HQ>1 | Low | Medium |
|
| PBDE-209 | HQ>1 | Low | Medium | |
| Benzothiazole | HQ>1 | Low-Medium | High |
|
| Triclocarban | HQ>1 | Low | Medium |
|
| Cyclomethicone 5 | HQ>1 | Low | Medium |
|
| Cyclomethicone 6 | HQ>1 | Low | Medium | |
| Atenolol | HQ>1 | Low | High – Very High |
|
| Chemical exposures (general) | HQ>1 | Low - Medium | Medium – Very High |
|
This analysis has focussed on emerging contaminants and issues, and as such it was not possible to assess a proportion of the potentially hazardous agents (semi-)quantitively in a meaningful way. There is very little known about microplastics in the terrestrial environment, and while they are likely present in sewage sludge, it is not possible to determine if people will end up being exposed to them or what the consequences of this exposure might be. Similarly, while the majority of pathogens potentially present in sewage sludge have been shown to pose minimal risk to human receptors, the significance of sewage sludge as a reservoir of antibiotic resistance is poorly understood.
Overall, the impacts of sewage sludge (when used correctly) on physical health outcomes is likely to be minimal and not significantly different to other organic soil amendments (e.g. animal manures). Impacts associated with quality of life and well-being (such as annoyance from malodour) can, however, be much more acute. These impacts are not exclusive to sewage sludge but are associated with a range of industrial and agricultural practices. In our opinion, physical health risks have been by and large managed through improvements in sludge treatment processes as well as best practice; however, the impacts on well-being have been largely ignored.
It should be noted that 'emerging' potentially hazardous agents is an ever-changing situation. The main hazards of concern today are likely to be superseded in the future. Since the 2008 report (SNIFFER 2008) we have seen the focus move from inorganic contaminants towards organics and pharmaceuticals, as well as 'novel' pathogens and antimicrobial resistance. Over the next 10 years, a different set of hazards are likely to become priority. Protecting public and environmental health is an on-going process.
Contact
Email: gary.gray@gov.scot
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