Weed management: a need for ecological approaches - Ecological Management of Agricultural Weeds - page 17

to a significant portion of acute pesticide poisonings in developing countries.
Hilje et al .(1992,p.79) reported that bipyridilium,chloroacetamide,dinitroa-
niline, phenoxy, picolinic acid, substituted urea, and triazine herbicides
accounted for 19% of the 787 pesticide poisonings registered in 1984 by the
Costa Rican National Poison Control Center. Similarly, Dinham (1993, p. 105)
noted that various herbicides were responsible for 22% of the acute pesticide
poisonings in the region of Limón, Costa Rica, in the first six months of 1990.
Hilje et al . (1992, p. 79) stated that the actual number of pesticide poisonings
in Costa Rica is higher than that reported to government agencies, but that
available data accurately reflect the percentage of poisonings attributable to
different types of pesticides.
Chronic health effects of chemical exposure can include cancer and disor-
ders of the immune, endocrine, neurological, and reproductive systems.
Unambiguous cause-and-effect relationships are often difficult to establish
for these types of health problems because a long lag period typically exists
between exposure to causative agents and presentation of clinical symptoms,
and because exposure to other chemicals or behaviors such as smoking may be
contributing factors. Epidemiological studies can be conducted, however, to
determine patterns of risk associated with exposure to herbicides and other
pesticides.
Thirty-nine herbicide active ingredients are classified by the US
Environmental Protection Agency (1999) as probable, likely, or possible carci-
nogens, and a number of epidemiological studies have examined possible
links between herbicides and cancer in human populations. Significant corre-
lations between herbicide use and several types of cancer were noted by Stokes
& Brace (1988) in a study of cancer deaths in 1497 nonmetropolitan counties
in the USA.The percentage of land area treated with herbicides in each county
was significantly correlated with the incidence of genital, lymphatic, hemato-
poietic, and digestive system cancers. Herbicide use had no relationship with
urinary system cancers, however, and was negatively correlated with respira-
tory system cancers.On Saskatchewan farms of less than 400 ha,death of male
farmers due to non-Hodgkin's lymphoma (NHL) rose significantly with
increasing numbers of hectares sprayed with herbicides (Blair, 1990; Wigle et
al ., 1990). No significant relationship was found on farms of more than 400
ha, where farmers may have been less likely to apply herbicides personally or
may have used aircraft for applications.
Hoar et al .(1986) reported that the incidence of NHL among men in Kansas
increased significantly with the number of days per year that they used herbi-
cides; men who used herbicides more than 20 days per year had a six-fold
higher chance of contracting NHL than did nonfarmers or farmers not using