Weed management: a need for ecological approaches - Ecological Management of Agricultural Weeds - page 14

American maize belt, Nelson & Jones (1994) noted that a substantial propor-
tion of sampled locations had at least one measurement of atrazine, cyana-
zine, or alachlor that was more than four times higher than maximum
contaminant or health advisory levels. Most community water systems in the
Mississippi River drainage basin are not equipped with technology that can
reduce herbicide concentrations to levels lower than government health stan-
dards (National Research Council, 1989, p. 101; Goolsby, Coupe &
Markovchick,1991; Nelson & Jones,1994).Consequently,the American Water
Works Association has expressed concern that costly additional treatment
systems, such as granular activated charcoal, will have to be installed in many
public water systems in the midwestern USA to address violations of the
federal Safe Drinking Water Act (Nelson & Jones, 1994).
Because certain herbicides can be harmful to aquatic organisms, “aquatic
life guidelines” have been set for several herbicides found in surface water.
Canadian standards,which are also used as nonenforceable benchmarks in the
USA,are 1 g L 1 for metribuzin,2 g L 1 for atrazine and cyanazine,8 g L 1

for metolachlor,and 10 g L 1 for simazine (Larson,Gilliom & Capel,1999).It

is clear from the data presented in Figure 1.4 that atrazine concentrations in
American rivers can exceed the Canadian aquatic life standard. Aquatic life
standards for other herbicides detected in rivers and streams are also often
exceeded (Larson, Gilliom & Capel, 1999).
An additional concern is how herbicides affect coastal ecosystems.Goolsby,
Battaglin & Thurman (1993) estimated that discharges of atrazine from the
Mississippi River into the Gulf of Mexico from April through August were
296000 kg in 1991,160000 kg in 1992,and 539000 in 1993 (a flood year).The
possible impacts of such discharges on aquatic organisms in the Gulf of
Mexico and elsewhere are inadequately understood and require more
research.
Herbicides and their degradation products are common contaminants of
groundwater in many agricultural regions (Hallberg,1989; Leistra & Boesten,
1989; National Research Council, 1989, pp. 107-9; United States Geological
Survey, 1999). In the USA, groundwater is used for drinking water by nearly
half of the total population and by more than 95% of the population in rural
areas (National Research Council, 1989, p. 105). Herbicides that have been
measured in wells of American agricultural areas at concentrations greater
than maximum contaminant or health advisory levels include alachlor, atra-
zine, cyanazine, 2,4-D, DCPA, dicamba, dinoseb, metolachlor, metribuzin,
and simazine (Hallberg, 1989). In a survey of private wells used for drinking
water in Ohio, Indiana, Illinois, West Virginia, and Kentucky, Richards et al .
(1996) detected chloroacetamide and triazine herbicides in 9.7% and 4.9% of