Potentially hazardous agents in land-applied sewage sludge: human health risk assessment

1. Introduction

Treated sewage sludge, also known as biosolids, has been beneficially recycled to agricultural land for many decades in the UK, Europe, the USA and other countries throughout the world. Recent data suggest that around 78% of the 3.6 million tonnes (fresh weight) of biosolids produced in the UK is currently recycled to agricultural land (Black et al., 2016). Biosolids are a valuable source of nitrogen and phosphorus, as well as other major and minor plant nutrients, and because of some conditioning processes have value as a liming material (SRUC, 2013). Biosolids also contain valuable quantities of organic matter and are therefore an important means of replenishing soil organic matter levels that can provide long-term benefits to soil structure and fertility. As such, the recycling of biosolids to land is recognised as being the best practicable environmental option by the European Union (EU) and UK Government in most circumstances.

However, partly due to complaints and concerns from communities reporting potential issues associated with the recycling of biosolids to land, a review of the existing legislation and procedures relating to the spreading of sewage sludge to land in Scotland was commissioned in 2014. This work was overseen by Scottish Government, SEPA and Scottish Water and brought forward several recommendations.

One key recommendation focused on the potential health impacts associated with sludge spreading and the lack of up to date, robust evidence. Most recently, a SNIFFER (Scotland and Northern Ireland Forum for Environmental Research) report in 2008 looked at human health and environmental impacts of the use of sewage sludge in land restoration and forestry and found no proven elevated health risks associated with the spreading of this material. The report also stated that incineration of sludge potentially presented "a higher risk to workers and the public." The SNIFFER 2008 report did not however cover storage or spreading to agricultural land or include many emerging issues such as the presence and spread of antimicrobial resistance genes (AMR) through the use of sewage sludge. It was therefore considered, in light of recent concerns expressed by the general public into odour, bioaerosols, diffuse pollution etc. that this topic should be re-visited.

Since the publication of SNIFFER 2008, several studies have been undertaken looking at potential health impacts associated with the use of sewage sludge. Arguably, of most relevance to this project has been work undertaken in the Unites States by the EPA (2014) "Bioscience Resource Project: Sewage Sludge (Biosolids) — land application, health risks, and regulatory failure". There have also been a large number of academic studies since 2008 (the search terms "sewage sludge or biosolids and human health" return almost 19,000 studies published since 2009 on Google Scholar). While the number of studies relevant to this project is far less (and many studies that seem relevant will not be of appropriate design), this does provide an indication of the level of new knowledge.

It is therefore now imperative that the evidence base provided in SNIFFER 2008 is not only updated, but also extended. In particular it needs to include common causes of complaint and emotive issues such as odour control, as well as 'emerging' contaminants including pharmaceuticals, personal care products, and AMR.

1.1. Objectives

The project aims to undertake the following objectives with oversight from a Steering Group consisting of Scottish Government, SEPA and Health Protection Scotland:

• Update the SNIFFER 2008 report with a focus on re-assessing and quantifying the human health implications and risks from sewage sludge storage, transportation and spreading on land (agricultural and non-agricultural land).
• Develop robust and effective evidence for potential impacts associated with spreading of sewage sludge on land, with emphasis on the potential effects strong odour can have on human health and well-being.