Pesticide Residues in Surface Water and Groundwater - Pesticides: Evaluation of Environmental Pollution - page 264

others. However, the absolute selectivity is difficult to achieve, and most pesticides create
some risk to human health. This results in them being potentially harmful to nontarget
organisms, and, therefore, they can be serious pollutants even in low concentrations. The
major factors that determine if a pesticide can be approved for use are rapid biodegrada-
tion and minimal environmental toxicity. That is why persistent organochlorine pesti-
cides were gradually withdrawn. They were replaced by organophosphorus (OPPs) and
organonitrogen (ONPs) pesticides, as they are less stable in the environment than organo-
chlorine compounds (Tankiewicz et al. 2010). The OPPs as a group vary considerably
in chemical and environmental properties (Larson et al. 1997). Most of the phosphorus-
containing organic compounds act as insecticides. Structurally, they are usually esters
and decompose very quickly (Tankiewicz et al. 2010). Because of their low persistence
and high effectiveness, these compounds are widely used as systematic insecticides for
plant, animal, and soil treatments (Tadeo et al. 2008). In 2001, 33,000 tons of OPPs were
sprayed onto crops in the United States (Kiely et al. 2004). ONP is the term covering a
large number of different compounds. When plant protection products are considered,
this term is usually used for carbamates and triazines. Carbamates are esters of carbamic
acid, used worldwide as insecticides, herbicides, fungicides, and plant regulators. They
are normally decomposed by soil microorganisms in 3-5 weeks. Triazine pesticides have
been synthesized to control broad-leaved weeds in a variety of crops. They are effective
at low dosages for destroying broad-leaved weeds in corn and other crops, and they can
be used in high dosage as soil sterilants. These compounds have substantial persistence
in soil (Tadeo et al. 2008).
World pesticide amount used exceeded 4.1 million tons in 2000 and 2001. Herbicides
accounted for the largest portion of total use, followed by insecticides and fungicides. Total
world pesticide amount used decreased in 2001 for all pesticide types. Pesticide amount
used in the United States in both 2000 and 2001 exceeded 0.5 million tons, in proportions
similar to those of world pesticide use. Ten most frequently used pesticides in the United
States are presented in Table 9.1. Glyphosate was the most frequently used pesticide in
2001, replacing atrazine which was the most frequently used agricultural pesticide for a
number of years (Kiely et al. 2004).

TABLE 9.1
The Most Frequently Used Pesticides in the US Agricultural Crop Production in the Years 2001,
1999, and 1997

2001
( × 1000 t)

1999
( × 1000 t)

1997
( × 1000 t) Pesticide Activity

Glyphosate Herbicide 36-41 30-33 15-17

Atrazine Herbicide 34-36 34-36 34-37

Metam sodium Fumigant 26-28 27-28 24-26

Acetochlor Herbicide 14-16 14-16 14-16

2,4-D Herbicide 13-15 13-15 13-15

Malathion Insecticide 9-11 13-15 NA

Methyl bromide Fumigant 9-11 13-15 17-20

Dichloropropene Fumigant 9-11 7-9 15-17

Metolachlor-S Herbicide 9-11 7-9 —

Metolachlor Herbicide 7-10 12-14 29-31

Source: From Kiely, T., Donaldson, D., and Grube, A. 2004. Pesticides Industry Sales and Usage. 2000 and 2001

Market Estimates. US Environmental Protection Agency: Washington, DC. http://www.epa.gov/pes-
ticides/pestsales/01pestsales/market_estimates2001.pdf (accessed 28 January 2011).