Sludge Watch ==> UK - study surveys long term impact ofagricultural sludge use

[Maureen Reilly]

Sludgewatch Admin:

The UK is spending about a million dollars on studies to look at heavy metal 
loading on land from sludge spreading, on uptake of metals into crops, on 
sludge impacts on microbes in the soil, on soil respiration and soil 
fertility.



see:

http://randd.defra.gov.uk/Default.aspx?Menu=Menu&Module=More&Location=None&ProjectID=10677&FromSearch=Y&Publisher=1&SearchText=SP0130&SortString=ProjectCode&SortOrder=Asc&Paging=10
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Edie News UK

Scientific study seeks to survey safety of sewage sludge (16 November 2007)

Heavy metals, sewage and mud may sound more like the key components of a 
rock festival, but are in fact the subjects of a study looking into the 
sustainable disposal toxin-rich sludge.

Since the 1990s, Defra has been conducting experiments to see how the 
poisonous heavy metals which accumulate in sewage sludge might impact on 
soil quality when the waste is spread on agricultural land.

Disposing of treated sludge in this way has a number of environmental 
benefits as it replaces valuable organic matter and avoids the need for 
incineration or landfilling, but there is also the potential danger of 
toxins contaminating land.

The tests were designed to calculate the effect of cadmium, zinc and copper 
in sewage sludge on micro-organisms in the soil.

The research team has now filed and interim report, which can be viewed on 
the Defra website, which suggests that the metals could have an impact on 
soil quality over the long term.

It also warns against over-egging the danger, as it points out that it would 
take over 100 years to reach the deliberately high concentrations of metals 
used in the experiment.

It also says that in practice the concentrations of metals reaching the 
sewage system has fallen considerably in recent years.

The long timescale over which the effects were projected means that there is 
good time, before there is any significant risk of damage occurring, to 
properly investigate the issues arising from the experiments so far.

It is important that this work is taken forward carefully to ensure that 
policy on sewage sludge spreading is based on sound science, said Defra.

Further work is now planned to understand the mechanisms behind the 
identified impacts and how these could be influenced.

http://www.edie.net/news/news_story.asp?id=13790&channel=0



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NEWS RELEASE
Ref: 419/07
Date: 14 November 2007Nobel House, 17 Smith Square, London SW1P 3JR
Out of hours telephone 020 7270 8960

Soil fertility experiments will help ensure sustainable use of sewage sludge 
on land
An investigation into the effects on soil quality and fertility of the heavy 
metals present in sewage sludge has published interim findings today. The 
results will help inform the sustainable recycling of organic material to 
land to improve soil quality.

Spreading treated sewage sludge on agricultural land provides organic matter 
and nutrients and maintains soil carbon, as well as offering what is in many 
circumstances the best environmental option for recycling of sewage sludge. 
The alternative disposal routes are landfill or incineration, both of which 
waste a potentially valuable resource.

Experiments started in the mid 1990s to examine the effects of cadmium, zinc 
and copper in sewage sludge on soil micro-organisms. The aim was to 
investigate long term impacts, and the metal-rich sludge was applied at 
elevated rates over 4 years to establish treatments that exceeded the 
maximum permissible soil metal concentrations detailed in the Sludge Use in 
Agriculture Regulations.  In operational practice, it would take longer than 
a 100 year period to reach these concentrations.

Headline results show that under certain conditions metal-rich sludge could 
impact upon some microbial groups, with implications for soil quality over 
the long term. The significance of the results will be considered in light 
of several factors, including:

The intensity of the sludge application in the experiments would not happen 
in the field, and the results need to be interpreted with caution and in 
light of modern practice;
The amount of metals entering the sewerage system has declined sharply in 
recent years, and the sludges used in the experiments do not represent 
current quality. The results therefore represent the potential impacts under 
a worst-case scenario; and
The long timescale over which the effects were projected means that there is 
good time, before there is any significant risk of damage occurring, to 
properly investigate the issues arising from the experiments so far.  It is 
important that this work is taken forward carefully to ensure that policy on 
sewage sludge spreading is based on sound science.
Further work is now planned to understand the mechanisms behind the 
identified impacts and how these could be influenced.

The interim results are published in Defra's Science and Research Projects 
pages:

Effects of sewage sludge on agricultural productivity and soil fertility 
(Phase III) - SP0130

Notes to editors
1.         A Review by an Independent Scientific Committee on the Rules for 
Sewage Sludge Application to Agricultural Land – Soil Fertility aspects of 
potentially toxic elements (MAFF, 1993) recommended that “further research 
was needed to examine the effects of heavy metals from sewage sludge on soil 
micro-organisms.”

2.         The experiment was set up in 1994 to determine the effects of 
sewage sludge additions to land on soil microbial populations and on soil 
function.  Soil micro-organisms are the portion of soil responsible for the 
breakdown of organic materials and nutrient cycling.  The trials have no 
relevance for health and safety aspects of sewage sludge recycling.

3.         The Defra research project was co-funded by the Scottish 
Executive, Welsh Assembly Government, Environment Agency and UK Water 
Industry Research.

4.         The regulations are:  The Sludge (Use in Agriculture) Regulations 
1989 (and the 1990 amendments thereto). These are supported by a 
departmental Code of Practice for Agricultural Use of Sewage Sludge (latest 
version 1996), which recommends a tighter soil limit for zinc.

5.         Since the trials began, changes in industrial practices and 
strict controls at source have led to considerable reductions in the 
concentrations of metals found in sludge from sewage works. The main inputs 
of metals now come from diffuse sources such as run-off and household use 
rather than industrial sources.

End

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