HUMAN HEALTH AND THE ENVIRONMENTAL IMPACTS OF USING SEWAGE SLUDGE ON FORESTRY AND FOR RESTORATION OF DERELICT LAND Task 3

HUMAN HEALTH AND THE ENVIRONMENTAL IMPACTS OF USING SEWAGE SLUDGE ON FORESTRY AND FOR RESTORATION OF DERELICT LAND
Task 3 – Site investigations
UKLQ09
August 2008

EXECUTIVE SUMMARY
Project partners: SNIFFER, SEPA, NIEA, Scottish Government, Forestry Commission, Health Protection Scotland

Use of the report
The technical document has been developed through a collaborative project, managed and facilitated by SNIFFER and has involved the members and partners. It provides background information, within the confines of the project brief, to support and inform member organisations and others.
Whilst the document is considered to represent the best available scientific information and expert opinion available to the consultant at the stage of completion of the report, within the confines of the specification given, it does not represent the final or policy positions of SNIFFER or any of its partner agencies, and it recognises that the historic practices regarding sewage sludge recycling discussed are not current practice within the UK.

Background to research

Although there is a great deal of research and scientific data on sewage sludge application to land, much of this relates to modest application rates on agricultural land. In recent years there has been a substantial increase in the amount applied to forestry, and to former opencast coal sites in the UK for purposes of land restoration. Application rates of sewage sludge have been considerably higher than traditionally practiced, and sludge has been applied using different techniques. There is concern that poorly managed practices could result in risks to human health, water, air and soil quality and to biodiversity. Public and political interest is high and this project will address the urgent need to review this activity and develop decision support systems and guidelines to ensure that the activities will not affect public health or adversely affect the environment.

Objectives of research

In detail, the project aims to:

carry out a detailed desk-based literature review;
undertake quantitative assessment of sites where sewage sludge has already been applied;
develop a site suitability and risk assessment procedure.

The objective of the report is to report on the findings from the completion of the second aim, the quantitative site assessment. Two reports were originally published in 2007 detailing the results of the desk-based literature review of the potential impacts of the application of sewage sludge on human health (Task 1) and the environment respectively (Task 2). A further two reports will be published covering the third project aim, outlining a decision support tool for the use of sewage sludge in land reclamation and forestry respectively (Tasks 4 to 6).

Key findings

The extensive soil survey and analysis undertaken at the four sites demonstrate that there has been no serious impairment to soil quality. The total phosphorus concentrations are rather high but this does not seem to manifest itself in the available phosphorus concentrations.
The analysis does demonstrate very clearly the homogenisation of soil properties with depth compared to both cultivated agricultural soils and semi natural soils. This is to be expected given the very intrusive and disruptive method of sludge incorporation to depths much greater than normally associated with sludge application to land. This does not replicate natural soil forming processes nor the natural distribution of organic matter or nutrients in soil.
Heavy metals from the applied sludge are likely to have been ‘diluted’ because they have been applied to a much greater volume of soil than normal. There is some evidence that soil metal levels are much lower than might be expected given potential metal levels in the applied sludge and the depth (based on the information provided) to which it has been incorporated. This could indicate that possibly some of the sludge has been incorporated to a greater depth than stated or that less sludge was actually applied.
The application method also masks the presence of highly organic and acid soils on the forestry sites due to the mixing of the uppermost horizons with subsoil and parent material.
There was no evidence of E.coli being found in any of the soil samples from the four study sites, and numbers of total coliforms were relatively very low and only found in a few of the samples. Hence, while it could be inferred that the potential risks were low, particularly over the longer term, in reality, too long a time period had elapsed since application of sewage sludge to make a meaningful assessment of this issue.
The perched water analysis identifies that the application of sewage sludge has had some negative influence on perched water quality on some of the sites, with high levels of phosphorus and ammonia in particular. However the effects identified do not appear to be substantial nor consistent. These inferences are based on highly limited data and it is not possible to say whether any of the variations in water quality identified are statistically significant.
The analysis carried out at all four sites indicates that the applied sludge poses no or minimal risk to human health.

Key words: Sewage sludge, Land Reclamation, Forestry, Soil, Environment, Human Health, Water

Copies of this report are available from the Foundation, in electronic format on CDRom at £20.00 + VAT or hard copy at £25.00, less 20% to FWR members.
N.B. The report is available for download from the SNIFFER Website

© SNIFFER 2008
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