20
Trace Elements in Abiotic and Biotic Environments
from seafood consumption is not significant. General consensus in the literature is
that about 85%–90% of the As in the edible parts of marine fish and shellfish is
organic As (e.g., AB, AC, and DMA) and that approximately 10% is inorganic As.
However, the inorganic As content in seafood may be highly variable. For example,
a study in the Netherlands reported that inorganic As comprised of 0.1%–41% of the
total As in seafood (Vaessen and van Ooik 1989).
The greatest threat to public health from As originates from contaminated groundwater. Inorganic As is naturally present at high levels in the groundwater of a number
of countries, including Argentina, Bangladesh, Chile, China, India, Mexico, and the
United States of America. Drinking water, crops irrigated with contaminated water,
and food prepared with contaminated water are the sources of As exposure. It is
particularly devastating in Bangladesh. Millions of tube wells were installed to provide pure water to prevent morbidity and mortality from gastrointestinal disease, but
the water was not tested for As contamination. According to survey data from 2000
to 2010, an estimated 35 to 77 million people in the country have been chronically
exposed to As in their drinking water, in what has been described as the largest mass
poisoning in history. The tube wells draw the As-containing groundwater from a
shallow depth of 10–70 m. Groundwater from depths >150 m usually contains less
As and can be a sustainable drinking water source. Between 2000 and 2003, 4.94
million tube wells throughout Bangladesh were tested for As and were marked as
safe or unsafe. Areas showing high proportions of unsafe wells (i.e., wells in which
As concentration in water is >50 μg/L, the Bangladesh drinking-water quality standard) are largely the same areas experiencing the highest As concentrations (often
>200 μg/L) (Flanagan et al. 2012).
Studies in other countries where the population has had long-term exposure to
As in groundwater indicate that 1 in 10 people who drink water containing 500 μg
of As/L may ultimately die from cancers caused by As, including lung, bladder,
and skin cancers. It is estimated that the lifetime risk of dying from cancers of the
liver, lung, kidney, or bladder while drinking 1 liter a day of As-containing water
at concentration 50 μg/L could be as high as 13 per 1000 persons exposed; the risk
estimate for 500 μg/L of As in drinking water would be 13 per 100 people (Smith
et al. 2000).
The Joint FAO/WHO Expert Committee on Food Additives (JECFA) established the provisional tolerable weekly intake (PTWI) of 0.015  mg/kg bw for
inorganic As (equivalent to 0.0021 mg/kg bw/day) (WHO 1989). But focused on
more recent data showing effects at lower doses of inorganic This PTWI for inorganic As was withdrawn by JECFA because it was not possible to establish a safe
exposure (WHO 2011b).
Cereals, fruits, vegetables, meat, poultry, fish, and dairy products can also be
dietary sources of As (Table 3.4), although exposure from these foods is generally
much lower compared to the exposure through contaminated groundwater. In seafood, As is mainly found in its less toxic organic form.
After Heitkemper et al. (2009), the average daily intake of inorganic As from rice
in the United States would be approximately 0.003 mg. Ethnic groups that consume
higher amounts of rice daily would have a daily intake of approximately 0.0105 mg
of inorganic As. In the United Kingdom, the population dietary exposure to total As