The local community in Esperance raised concerns about
environmental contamination following the death of a number of native
birds during late 2006 and early 2007. Forensic investigations of dead
birds suggested that lead may have been the causative agent. Subsequent
investigations by government agencies included analyses of lead and
nickel concentrations in air, rainwater, soil, dust, swabs, plants,
birds and human blood.
There was concern in the Esperance community about the potential
impacts of the contamination on the resident's health.
Subsequently, the Department of Environment and Conservation (DEC)
retained Golder Associates Pty Ltd., (Golder) to undertake a human
health and ecological risk assessment (risk assessment) using the
information collected during the investigation of lead and nickel
contamination in Esperance. As a first step, Golder undertook a Data Gap
Analysis (DGA) to assess the suitability of the available information
for the risk assessment. While a large volume of information was
available, some was found to be unsuitable for risk assessment for a
variety of reasons.
MATERIALS AND METHODS
Golder followed State and National risk assessment guidance (1).
Risk assessment is a systematic process for collecting, evaluating and
integrating biological and environmental information comprising a four
step process: issue identification, hazard assessment, exposure
assessment and risk characterisation. The issue identification stage
identifies the issues that can be assessed through risk assessment and
clarifies the context for the risk assessment. An important component of
issues identification (sometimes referred to as problem formulation) is
the development of a Conceptual Site Model (CSM), a tool that can help
in identifying sources, exposure pathways and receptors on which to
focus a risk assessment.
Normally environmental sampling and analyses would occur once the
CSM has been developed. Contaminant information available for the
Esperance risk assessment was collected in response to an apparent
pollution incident and it was unclear whether or not the information was
suitable or sufficient for assessing health risks to human and
environmental values. Thus, Golder considered that a systematic
assessment of the information through a Data Gap Analysis (DGA) was
necessary to assess its usability in the risk assessment.
The CSM developed for the Esperance town site considered
contaminants of concern in food, soil, sediment, water, ambient air and
deposited dust; uses of these media by the receptors; and exposure
variables such as land uses, human exposure routes, ecological exposure
routes and human and ecological receptors.
The information received from DEC comprised 80 reports of data
collected by a number of government and non-government organisations,
including Esperance residents. The data were ranked according to
national guidelines (1) into one of three categories ranging from low
(higher uncertainty) to a high confidence level (lower uncertainty)
depending on the level of confidence that could be assigned to the
outcome of the risk assessment based on the data.
Golder identified a number of receptor groups in the CSM that
included human and terrestrial and aquatic ecological receptors.
Exposure scenarios considered for human receptors included residential,
recreational park users and subsistence users. Terrestrial ecological
receptors included terrestrial plants, mammals, birds, other vertebrates
and invertebrates. Freshwater ecological receptors were not considered
because of the distance to the nearest freshwater body from the
Esperance town-site. Marine ecological receptors included marine plants,
mammals, birds, fish and benthic species. Receptor exposure pathways
included ingestion, inhalation or dermal exposure to soil, dust or
rainwater, including food chain pathways.
Following are examples of data to which different degrees of
confidence were assigned in the DGA.
Data that provided a higher degree of confidence for inclusion in
the risk assessment included the results of rain water analysis. These
comprised a large data set of targeted sampling in the Esperance town
site that also provided an indication of the distribution of
contamination. The rain water was a defined body of water with a
relatively stable level of contaminants and the results provided a
reasonable basis for estimating exposure by ingestion and dermal
Results of soil sampling and analysis provided a medium degree of
confidence for use in the risk assessment. Soil samples were generally
collected close to the Port within the Esperance town site and along the
railway transport route as part of the response to the pollution
incident. The data did not necessarily reflect a spatial distribution of
lead and nickel concentrations in soil across the entire town site. This
was taken into consideration during the risk assessment by the use of
realistic concentration statistics such as the 95% upper confidence
limit of the mean.
Some data were collected under circumstances where confidentiality
agreements did not allow disclosure of sample details to third parties
e.g., the identity of donors of blood for blood lead levels analysis.
This limited some of the analyses Golder was able to undertake, without
modifying the data. However, Golder was able to undertake a co-location
analysis of these and other data once the names and residential
addresses were codified by appropriately authorised people and hence
assess relationships between lead and nickel concentrations and distance
from the port in 250 m increments.
Various data supplied were assessed as having a higher level of
uncertainty hence a lower level of confidence for use in the risk
assessment. Data from swab samples collected inside Esperance residences
and ceiling dust samples from roof cavities were supplied. These data
were collected for "forensic" rather than risk assessment
purposes. Due to the nature of swab or ceiling dust samples, it is
difficult to estimate inhalational exposure since the swab samples
measure dust loads on surfaces or ceiling spaces and not concentrations
in indoor air. Nonetheless, we used a set of conservative assumptions to
estimate concentrations of lead and nickel in indoor air that could be
used in the risk assessment.
A lower level of confidence was associated with body burden data
supplied for lead and nickel in birds. Although the large number of bird
deaths reported in Esperance was suggestive of a problem or illness, it
was difficult to assess the relationship quantitatively from the limited
numbers of dead birds that were available for analysis. In addition,
birds are not a static organism and their exposure is difficult to
estimate due to anticipated variations in habitat and diet.
The majority of soil and plant samples were collected in
residential zones around the town site, as opposed to areas of open
space or bushland where wildlife are more likely to live. Body burden
data for lead and nickel in mammalian wildlife in the Esperance area
were not collected. Subsequently mammalian exposure to lead and nickel
could not be directly assessed and was instead evaluated using a food
chain modelling approach. Hence, the assessment for land animals was
considered to have a lower degree of confidence.
The general aim of a risk assessment is to collect data in a
systemic manner from environmental media and biological systems and
assess the risks to human or ecological health. The development of CSM
helps identify the contaminants of interest, sources of contamination,
pathways of exposure and receptors of interest, thus facilitating the
development of a sampling and analysis plan for the risk assessment
(proactive sampling). This approach was not possible in the case of
Esperance, since the decision to undertake a risk assessment was taken
after the majority of data had already been collected in response to the
bird deaths (reactive sampling).
While a considerable proportion of the information available could
be used in the risk assessment, the degree of confidence associated with
the results was variable and in some cases was lower than may have
otherwise been if proactive sampling had been undertaken. Thus
conclusions were limited in scope and outcome for some issues that were
identified as a concern in the CSM.
Whilst proactive sampling may have resulted in a higher degree of
confidence in the result than reactive sampling, the data collected in
response to the pollution incident were usable and sufficient to draw
conclusions about the potential effects of the contaminants on the
residents and ecology of Esperance. These conclusions need to be placed
in the context of the degree of confidence in the results obtained.
This project was funded by the DEC.
(1.) National Environmental Health Council (enHealth Council),
2002. Guidelines for assessing human health risks from environmental
hazards. Commonwealth of Australia.
Sarah Taylor, Chelsea Papadopoulos, Sarah Vieillet and Peter Di
Department of Environmental Services, Golder Associates Pty Ltd,
P.O. Box 1914, West Perth WA 6872 Australia
Corresponding Author: Sarah Taylor, Department of Environmental
Services, Golder Associates Pty Ltd., P.O. Box 1914, West Perth WA 6872
Australia Tel: +61 (8) 9213 7600 Fax: +61 (8) 9213 7611