Agricultural-Based Food Production Geoenvironment Stressors - Sustainable Practices in Geoenvironmental Engineering - page 185

in Western Europe. Dating of 210 Pb in Tahiti has allowed the determination of the accu-
mulation of phosphorus in the sediments. The steps included exchangeable, iron-sorbed,
carbonate, marine organic, and terrigenous phosphorus forms. In the 1950s, terrestrial
phosphorus increased signiicantly due to both soil erosion and waste discharges.
The conversion of ammonia to nitrate lowers soil pH, particularly in northeastern
Canada and Scandinavia (Chamley, 2003), where the bedrock formations are siliceous.
The acidity increases the mobility of the toxic components, aluminum and manganese.
This can diminish vegetation and plant growth and increase soil erosion.
Due to its charge, phosphorus binds to soils but will leach from sandy soils with low
levels of clay, oxides, and organic matter. Surface runoff will most likely cause contamina-
tion of streams and lakes, whereas groundwater contamination by nitrates is more likely
since these anions are held more weakly by negatively charged clayey soils than phos-
phorus. Nitrate diffusion in the groundwater is very slow, in the order of 1 m/year. Thus,
the impact from excessive fertilization of the soil may only be seen in the groundwater a
decade later.
Inorganic fertilizers and other soil amendments such as animal manure and biosol-
ids contribute to elevated levels of N and P in the environment. Inorganic fertilizer use
increased by 20- and 4-fold from 1945 to 1980. Their use has since leveled off. Animal
manure contributes 6.3 million tonnes of N and 1.8 million tonnes of P compared with 10.8
million tonnes of N and 1.8 million tonnes of P from inorganic fertilizers (USGS, Circular
1225, 1999). About 15% of shallow groundwaters sampled beneath agricultural areas were
above the acceptable levels for nitrates.
In the Australian government-funded project to study the movement of phosphorus in
soils supplemented with piggery efluents (Redding, 2005), soil samples were taken down
to 5 cm in areas with and without the efluent amendment. Leaching was not signiicant if
correct management procedures were used, but it did occur if application rates were exces-
sive. Signiicant adsorption of the phosphorus occurred in the top 5 cm and phosphorus
runoff readily occurred from surface soil.
6.3.2.2 Pesticides
Pesticides are chemicals that have the purpose of eliminating (controlling) “pests” and are
classed as biocides . Most of these are considered as toxic chemicals that are injurious to
human health and other biotic receptors. There are several types of pesticides such as her-
bicides, insecticides, fungicides, rodenticides, verucides, etc., each of which is used directly
for control of speciic “pests.” Herbicides are used for controlling unwanted plants, insec-
ticides are used to control insects etc. They have been used since the nineteenth century in
the form of lead, arsenic, copper, zinc salts, and nicotine for insect and disease control. Since
the 1930s and 1940s, with the introduction of 2,4-D and DDT, agricultural use has increased
substantially. It has been reported that worldwide use of pesticides is approximately 2.4 bil-
lion kg (USEPA, 2006, 2007). The Database on Pesticides Consumption called FAOSTAT (United
Nations Food and Agriculture Organization, 2003) which is maintained by the United
Nations' FAO provides information on the use of speciic pesticides within each country.
Although pesticides have enhanced crop yields, concerns are increasing regard-
ing their effects on the health of humans and animals and their transport in the envi-
ronment. Levels of contamination of surface streams and groundwater increase with
increased nutrient and pesticide use (USGS, 1999). Agricultural streams show the highest
concentrations of pesticides. Herbicides are the most frequent pesticides found in agri-
cultural streams and groundwater. Atrazine (C 8 H 14 ClN 5 ), deethylatrazine (C 6 H 10 ClN 5 ),