Guidelines for Developing National Strategies to
Use Monitoring of Local and Diffuse Soil
Contamination as Environmental Policy Tools
Professor Mark Kibblewhite
(mark@mksoilscience.eu)
INTRODUCTION
• Local soil contamination from historic and present misuse, disposal
and spillage of materials may present an unacceptable risk of harm to
especially humans and water resources.
• Diffuse soil contamination occurs over wide areas, generally at lower
levels than local soil contamination; it may present risk of chronic
harm to the soil system itself, humans, water resources and
biodiversity.
Monitoring of local and diffuse soil contamination requires different
approaches and these are considered separately.
LOCAL SOIL CONTAMINATION
Strategy for local soil contamination
• Define unacceptable risk from local soil contamination
• Prioritize resources to sites presenting most risk to humans,
surface and ground waters and ecosystems
• Implement and monitor effectiveness of policy actions with
targets to assess and drive progress
How much contamination is acceptable?
• It is better to adopt a risk and not hazard-based approach. In this
case:
• the mere presence of a hazardous contaminant at any level does not in itself
indicate unacceptable contamination
• acceptability should be assessed in relation to risk of harm to specific
receptors (e.g. humans, natural waters, ecosystems).
• A risk-based approach allows site-specific decision-making and
avoids land being designated as having unacceptable local soil
contamination, when there is no unacceptable risk arising under its
current or planned use.
Possible Source-Pathway-Receptor linkages
Ingesting
dust
Ingesting
soil
Inhaling
vapour
Soil transfer
From garden
To house
Inhaling
vapour
Rising
vapour
Wind blown dust
Rising vapour
Eating contaminated
vegetables and
ingesting soil
Skin contact
with dust
Skin contact
with soil
Plant uptake
Illustration of human exposure from contaminated garden soil
Defining unacceptable risk from local soil
contamination
Unacceptable risk of harm
requires the definition of both
unacceptable harm and an
unacceptable probability of
exceeding this harm
This is achieved in a four steps.
1. Identification of the subject that is at risk
of harm (the receptor)
2. Identification of the type of harm that may
be caused by exposure of the receptor
3. Definition of a quantitative measure of risk
of this harm
4. Definition of the unacceptable level of risk
of harm.
EXAMPLE
1. The risk of harm to human health from a
contaminant X could be assessed in
relation to risk of harm to a 6 year old
female child
2. The type of harm that may result from
exposure to contaminant X could be
disease Y
3. The measure of risk of harm could be the
lifetime chance of such a child contracting
Y, relative to that for the wider population
of non-exposed children
4. A policy decision might be made that any
increase in the incidence of the disease
with a probability of more than 1 in
100,000 is unacceptable.
Managing local soil contamination
Sequential steps (at individual
sites)
1.
2.
3.
4.
5.
preliminary studies
preliminary investigation
main investigation
options appraisal
implementation of
remediation strategy
Targets should refer to the
number / percentage of sites
at which these steps are
completed
Metrics for monitoring local soil contamination
Metric
Total number of sites undergoing risk assessment or risk management (i.e. all sites within
inventories)
Number of sites with preliminary studies in progress
Percentage of total number of sites with preliminary studies in progress
Number of Potentially Contaminated Sites
Percentage of the total number sites currently identified as Potentially Contaminated Sites
Number of Contaminated Sites
Percentage of the total number sites identified as Contaminated Sites
Number of sites where a remediation strategy is being implemented
Percentage of the total number of sites where a remediation strategy is being implemented
Number of sites incurring costs within expenditure categories
Monitoring local soil contamination
• Designate a single coordinating institution
• Implement data collection exercises at intervals of no less
than five years using an unchanging questionnaire
• Establish a central inventory of data on sites of local soil
contamination
Actors
Central Government (responsible
Ministers and their officials)
Activities
Outputs (Examples)
Setting an overarching policy Key policies, e.g.:
framework
1. Avoid new contamination
2. Risk-based approach, focusing resources on higher risk sites
3. Polluter pays principle applies, but with financial and legal incentives to
encourage site assessment and management
4. Local-level regulation to encourage integrated actions by land owners /
managers / developers and regulatory authorities
Legislature
Designing and enacting a
Legislation and statutory regulations, e.g.:
national legislative regime 1. Legal definitions e.g. of “contaminated site”
2. Responsibilities
3. Liability
Central Agency (e.g. Environmental Developing and maintaining 1. Regulatory and technical procedures for assessing and managing sites of
Protection Agency)
technical guidance;
local soil contamination
monitoring progress
2. Definition and publication of intervention values for contaminants
3. Technical expertise for ‘difficult’ sites
4. Operation of national monitoring system for local soil contamination
1. Land owners / managers /
Identifying sites; assessing 1. Systematic identification of possible sites of unacceptable local soil
developers
risks; defining site
contamination
2. Regional / municipality
management plans
2. Preliminary studies / preliminary investigations of candidate sites
departments for development
(according to regulations
3. Main investigations of sites where required
control (spatial planning) and
defined by central agency) 4. Designation of sites as ‘contaminated land’ (by regional / municipal
environmental protection
authorities)
3. Technical experts and specialized Implementing and signing- 1. Evaluating options for management of contaminated sites and agreeing
contractors
off site remediation
detailed plans
4. Citizens and stakeholder
(according to regulations
2. Completing and confirming success of site plans.
DIFFUSE SOIL CONTAMINATION
• Diffuse soil contamination is
widespread and results from the
transfer of contamination from
other environmental
compartments, such as air and
water, as well as the use of
chemicals on land and the
spreading of organic and other
wastes.
• A precautionary policy position is
that diffuse soil contamination
should be minimized where
feasible and economics allow.
Purpose of monitoring diffuse soil
contamination
• Is diffuse soil contamination an
actual or potential risk (e.g. to
food production and / or water
quality)?
Strategy for diffuse soil contamination
• Define priority contaminants
• Inform decisions by
assessing the spatial
distribution and temporal
trends in contamination
• Integrate decisions with
wider environmental policy
to assess where to focus
control
Type of contaminant Examples (potential
priority
contaminants)
Cadmium,
Heavy metals
Chromium, Copper,
Lead, Mercury
Nickel, Zinc.
Arsenic, Antimony,
Metalloids
Selenium
Persistent Organic
Poly-Chlorinated
Biphenyls (PCBs),
Pollutants
Poly-Aromatic
Hydrocarbons
(PAHs), Dioxins,
Furans, banned
pesticides
Operational steps for monitoring
• Designate a single
coordinating institution
• Define quantitative
performance
requirements
• Confirm that the chosen
design is fit for purpose
• Adopt formal procedures
and protocols
• Maintain a central
database and sample
archive
Technical approach to monitoring diffuse soil
contamination
• Sampling soil over large areas
followed by testing of samples
for priority contaminants
Measurement performance specification
• Absolute detection limit i.e. the minimum level of the contaminant
that can be detected (mg kg-1);
• Dynamic range over which measurement of levels of the contaminant
are required (mg kg-1);
• Maximum error allowable e.g. specified as the standard deviation of
measurements of level of contaminant at 80% of the dynamic range
(mg kg-1);
• Detection limit for a change in level of contaminant at e.g. 50% of the
dynamic range, over a specified period (mg kg-1y-1).
Design of sampling network
• Invest in a thorough investigation of the expected measurement
performance of options using statistical modeling.
• A model approach locates sampling sites e.g. at the nodes of a
regular grid. A classical approach selects sites randomly from within
strata (categories of possible sampling sites) representative of e.g.
different land use / cover, geology, etc.
• On balance, it is recommended that countries establish systems
based on regular grids as these are more flexible to meet future
needs. A European-wide project aiming to develop a continental scale
soil monitoring system (ENVASSO) recommended a minimum
sampling density of 1 site per 300 km2.
Sampling and testing
• Large variations in levels of diffuse contamination of soils are
observed at field scales (1-10m) and it is essential to sub-sample an
adequate area at each location.
• Archive samples so that they can be re-tested or tested for additional
contaminants at a later date
• Standard ISO testing methods should be used.
• Laboratories should meet international performance standards by
having auditable traceability of measurements, quality control
systems incorporating standard reference materials, and participation
in inter-laboratory comparability exercises.
At what level does diffuse soil contamination
present unacceptable risk?
• If the contaminant does not
occur naturally then its level
should be as ‘low as practicable’
• If the contaminant occurs
naturally then account has to be
taken of background
“contamination” . For example, a
‘level of concern’ could be set at
two times the 90th percentile of
the non-urban background level.
Land cover Soil-forming
material
Urban
All
Metal
Cd
Pb
Agriculture Mudstone
Cd
Pb
Chalk till
Cd
Pb
Sandstone / Cd
Mudstone / Pb
Shales
Mean +/- 2 Median +/- 10th to 90th
standard
median
percentiles
deviations absolute
deviations
0.1-2.3
11-370
0.3-1.9
14-110
0.2-1.3
9-65
0.3-2.3
14-320
0.2-2.0
17-210
0.4-1.5
17-74
0.2-1.1
11-48
0.2-1.8
18-220
Background “contamination”
0.2-1.4
28-140
0.4-1.4
23-89
0.3-1.0
13-42
0.2-1.4
28-240
Concluding reflections
Soil monitoring systems are an essential part of integrated
environmental management
The specification of soil monitoring systems should be carefully
developed and design options fully evaluated before implementation
Establishing a permanent central secretariat is critical to the efficiency
and enduring good performance of soil monitoring systems