Groundwater in the Great Lakes Basin

Atrazine
Atrazine is an extensively used pre- and post-emergence
weed control agent, especially for corn crops
and rapeseed in Canada, corn and sorghum in the
United States. Its use will likely increase with the
increased production of corn to make ethanol. In some
areas it is the pesticide most likely to be found in
concentrations above health criteria in groundwater.
Most human exposure is through drinking water
rather than residues in food. Nausea and dizziness
have been reported after drinking water contaminated
with unspecified levels of atrazine. Atrazine is
considered not classifiable as to its carcinogenicity
to humans by IARC (2007) and it is not on the NTP
(2005) carcinogen list. Atrazine has been shown to
be carcinogenic in rats. It is genotoxic in only a few
test systems. Atrazine has been shown to produce
changes in mammalian steroid metabolism (GCDWQ,
04/1993) and is a known endocrine disruptor (State
Environmental Resource Center, 2004). The acceptable
daily intake (ADI) for atrazine is based on the
no observed adverse effect level (NOAEL) for several
endpoints divided by an uncertainty factor of 1,000. The
MAC has been set on this basis at 5 µg/L for the sum of
atrazine and its metabolites (GCDWQ, 04/1993). The
MCL for atrazine is 3 µg/L (U.S. EPA, 2007a).
A survey of 1,285 farm wells in Ontario by Agriculture
Canada in the fall of 1991 found that atrazine was
the most common of four pesticides detected. 7.1% of
wells contained atrazine or deethylatrazine, one of
its metabolites. The median concentrations were 0.4
µg/L for atrazine and 0.35 µg/L for deethylatrazine; the
maximum concentrations were 18.0 and 4.4 µg/L respectively.
A repeat survey in the summer of 1992 found a
higher percentage of detections, 10.5% (126 wells) and
6.3% (76 wells), respectively (GCDWQ, 04/1993).
In July 2005 the results for nearly 16,000 private wells
tested by an immunoassay screen for atrazine were
mapped by the Wisconsin Department of Agriculture,
Trade and Consumer Protection. 40% of private wells
had atrazine detections; 1% of private wells were above
the MCL of 3 µg/L for atrazine and three of its metabolites.
7,000 well-water samples were tested by full gas
chromatograph techniques. 25% had detectable atrazine;
5 % were above the MCL (Wisconsin DNR, 2006).
Aldicarb
Aldicarb is an insecticide that was widely used to
control a variety of insects, mites and nematodes. Its
use in Canada and the United States is now restricted.
Aldicarb is one of the most acutely toxic pesticides,
producing symptoms of dizziness, weakness, diarrhea,
nausea, vomiting, sweating, abdominal pain, blurred
vision, headache, muscular fasciculations, convulsions,
paralysis and dyspnea. It is rapidly eliminated
from the body so that episodes of acute poisoning are
usually short lived. Several studies of a Wisconsin rural
population showing an immunological effect had some
methodological limitations. The dose of aldicarb was
not calculated on a body weight basis; half the control
group was on municipal water rather than low aldicarb
well water. The presence of other contaminants in the
well water was not determined in the original study.
There is some evidence of immunotoxic effects of
aldicarb in animal studies. Aldicarb has not produced
increased tumour incidence in carcinogenicity
bioassays in rats and mice. Aldicarb is considered not
classifiable as to its carcinogenicity to humans by IARC
(2007) and it is not on the NTP (2005) carcinogen
list. Aldicarb has an estimated NOAEL of 10 µg/kg bw
per day for inhibition of red blood cell cholinesterase
and sweating based on the LOAELs observed for these
acute effects in a human volunteer study with men and
women. The ADI of 1 µg/kg bw per day has an uncertainty
factor of 10 for the variability in human populations.
The MAC is calculated at 9 µg/L based on the
ADI of 1 µg/kg bw per day for a 70-kg adult drinking
1.5 litres of water per day with a 20% allocation of
exposure to drinking water (GCDWQ, 02/1987). There
is no current U.S. EPA MCL for aldicarb.
Aldrin and Dieldrin
Aldrin and dieldin are chlorinated hydrocarbon insecticides
that have not been used except as an underground
termiticide since the mid-1970s, and that use ceased in
about 1990. Aldrin is converted to dieldrin in the environment.
Dieldrin is more stable and highly persistent.
Aldrin and dieldrin bioaccumulate in adipose tissue.
They are highly toxic to the human central nervous
system and liver. In samples of human breast milk (n
= 497) a Canada-wide survey found 94% contained
detectable levels of dieldrin (detection limit 0.04 ng/g).
The median concentration was 0.26 ng/g. Aldrin and
dieldrin are considered not classifiable as to their
carcinogenicity to humans by IARC (2007) and they
are not on the NTP (2005) carcinogen list. The ADI of
0.0001 mg/kg bw per day for both pesticides is based on
a NOAEL of 0.025 mg/kg bw per day in rat studies with
an uncertainty factor of 250. The MAC of 0.0007 mg/L
is calculated with this ADI for a 70-kg adult drinking
2 litres of water a day with 20% of aldrin or dieldrin
exposure allocated to drinking water (GCDWQ, 1994).
There is no current U.S. EPA MCL for aldrin or dieldrin.
Chlorinated solvents
Chlorinated solvents, such as tri- and tetrachloroethylene,
are widely used for metal degreasing and dry
cleaning. These volatile organic compounds (VOCs)
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