Introduction
Arsenic contamination of groundwater in Bangladesh
continues to be a widespread problem despite the best
international efforts of many countries including
Australia. Recent research has been directed to
studies of the transfer of As from groundwater to
soil to crops and the subsequent risk posed to human
health from ingestion. Extensive groundwater contamination
can have long term effects on the
environment and the landscape when extensively used for irrigation. Consequently this can have a
direct effect on human health when the primary use
of the landscape is to produce crops for human
consumption. Thus water contamination, soil contamination,
food contamination, and ultimately
human health are all interdependent. This interdependence
together with the heterogeneity in the soil
and groundwater environments has limited the
extrapolation of current research findings to the
landscape level because current research findings
are based on site specific risk investigations of As
exposure. A further constraint with the application of
published data to the landscape level is that limited
spatial/geographic information system (GIS) based
models currently exist which are capable of
incorporating site specific data on As in various
environmental media with the predictive capacity for
As contamination at the landscape level. This paper
reviews the current trends in risk assessment of As
with particular emphasis on the potential application
of GIS to human health and landscape level risk
assessment.
Arsenic is a widespread contaminant in the
groundwater aquifers of Bangladesh due to natural
geological formations (Islam and Nehaluddin 2002).
Arsenic occurs naturally in two main forms, arsenite
As(III) and arsenate As(V), where As(III) is considerably
more toxic than As(V) (Smith et al. 1998).
Under certain environmental conditions As can be
both bioavailable and mobile and can accumulate in
edible crops and fodder. Consequently ingestion of
affected crops and vegetables, meat from animals
ingesting contaminated fodder, and drinking of
contaminated water can potentially pose a serious
threat to human health. The recent large scale
incidents of human As poisoning in South East Asian
countries has led to a major socioeconomic, health,
and management crisis (Hassan et al. 2005). These
incidents are of international importance because
exposure to As is not a localized phenomena and is
not occurring in isolated areas or from point sources,
but is rather occurring at the landscape level.
Landscape has typically been defined in the
ecological framework as assemblages of habitat,
community, and its dynamic structure, function, and
spatial pattern (Forman and Gordon 1986, Hsu and
Cheng 1999). In this review paper landscape is
defined as a spatial extent and structure of a region
encompassing landuse and physiographic (i.e.,
terrain) as well as administrative boundaries. It is
therefore anticipated that the landscape will encompass
an area larger than a single village and that, for
chemical contaminants, landscape level risk can be
defined as the probability that an exposure event
occurs and causes potential impairment of human
health. Moreover, landscape level risk correlates the
environmental chemistry of contaminants with human
activities, management practices, and the subsequent
toxicological consequences. Previous authors have
stressed the need for a landscape level As risk model
due to the large spatial and temporal variation of As
concentrations in the environmental media (soil,
groundwater, and plants) with geographic region and
numerous different exposure pathways.