HUMAN HEALTH AND THE
ENVIRONMENTAL IMPACTS OF USING SEWAGE SLUDGE ON FORESTRY AND FOR
RESTORATION OF DERELICT LAND
Task 2 –
Literature review of environmental and ecological impacts
Project partners: SNIFFER, SEPA, NIEA, Scottish Government, Forestry
Commission, Health Protection Scotland
of the report
The technical report 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 sewage 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:
The objective of the report is to fulfil the first aim in relation to
the environmental and ecological effects of spreading sewage sludge on
- 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.
Key findings and
The majority of the available literature and research identified
relates to the application of sewage sludge to agricultural soils and
due to significant difference in the soils, the sewage sludge,
application techniques and rates involved, it is often difficult to
extrapolate these findings to the use of sewage sludge in forestry and
The application of sewage sludge improves the physical properties and
fertility of soil. The potential impact on soil physical
properties is dependent on the original texture and organic matter
content of the soil and improvements in structure are not linear with
There is potential for negative impacts on soil physical properties due
to the blockage of pores by the sewage sludge itself or the associated
microbial growth, and the potential formation of crusts.
Although a number of the pollutants within sewage sludge have the
potential to accumulate within the soil there is no evidence of direct
impact on soil physical properties. However, soil quality may
be affected indirectly through negative impact on soil organisms.
Improvements in the soil physical structure associated with sewage
sludge amendments can decrease soil leaching through reduction of
preferential transportation routes, and reduce runoff and sediment loss
through improved infiltration and structural stability.
Leaching of sewage sludge applied pollutants to groundwater, except
nitrogen, appears to be limited. However, the depths of
incorporation involved at some land reclamation and forestry sites
requires detailed consideration of the depth to groundwater and soil
properties below the incorporation depth.
For the majority of pollutants considered there appears to be greater
potential for transport to surface water, dissolved in runoff or
attached to particles carried in runoff or by wind, than to ground
water via leaching.
Application of sewage sludge often causes an increase in the soil
population, its activity and its mineralization capacity, with the
level of response being dependent on the original composition of the
soil. However, application of sewage sludge at high rates
which contain significant concentrations of certain pollutants has been
shown to have a negative impact on soil biodiversity and its
Application of sewage sludge can have positive impacts on biodiversity
of fauna and flora through addressing potential deficiencies in soil
fertility, plants and animals. Excess levels of pollutants
have however been shown to negatively impact the biodiversity of
terrestrial and aquatic flora and fauna. The potential for
bioaccumulation through the food chain of pollutants applied to the
soil via sewage sludge application for forestry and land reclamation
appears to be minimal.
The implications of pollutants associated with sewage sludge on
biodiversity requires further research, especially in relation to
potential additive toxic effects through interaction of components
within sewage sludge and long term exposure impacts
The literature shows that the application of sewage sludge to land can
lead to the emission of ammonia and the major greenhouse gases, carbon
dioxide, methane and nitrous oxide. In comparison to other
outlets for the disposal of sewage sludge such as combustion the
application of sewage sludge in land restoration and forestry may
represent a carbon sink.
There is potential for the other components of sewage sludge (e.g.
heavy metals and organics) to be lost from the soil to air via
volatilisation, however it is believed the impact on air quality should
be minimal compared to background levels present in the air.
These conclusions are based on the rates and method of application
utilised in agriculture further research is required in relation to the
rates and application methods associated with land reclamation and
Sewage sludge application in land reclamation and forestry can be
appropriate and beneficial, provided appropriate guidelines are
followed to minimise environmental and ecological damage and maximise
the potential benefit. The application of sewage sludge to
land may require reconsideration at a later date in light of any new
information regarding potential environmental and in particular
ecological impacts of the constituents of sewage sludge and/or sewage
sludge as a whole.
Key words: Sewage
sludge, Environment, Forestry, Land Reclamation, Biodiversity
Copies of this report are available from the Foundation, in electronic
format on CDRom at £20.00 + VAT or hard copy at
£35.00, less 20% to FWR members.
The report is available for download from the SNIFFER Website
© SNIFFER 2008
All rights reserved. No part of this document may be
reproduced, stored in a retrieval system, or transmitted, in any form
or by any means, electronic, mechanical, photocopying, recording or
otherwise without the prior permission of SNIFFER.