Environmental Engineering Reference
In-Depth Information
6.5.2 Impact of Soil Additives
Various agricultural and industrial wastes are utilized as amendments for agricultural
soils. The addition of these amendments as aids to plant growth by and large generates
chemical stressors that impact on the applied soil in a way that can threaten human health
and other biotic receptors because of contamination of groundwater and receiving waters
and uptake by plants. Irrigation with reclaimed sewage water is practiced in arid and
semiarid areas. In Israel, irrigation for 28 years with sewage efluents has led to the accu-
mulation of cadmium, copper, nickel, and lead in the top soil layer in coastal plain soils
(Banin et al., 1981). Signiicant amounts of these metals accumulated in the oxide fraction of
the soils. The amounts recorded show that (a) for Cd the percentages retained varied from
9% to 20%, (b) for Cr, this varied from 5% to 11%, (c) for Cu, the variation was from 16% to
23%, (d) for Ni, this was from 10% to 14%, and (e) for Pb, the variation was from 1% to 3.9%.
Approximately 20% to 45% of produced sewage sludge is added for agricultural use in
the United Kingdom, Germany, and United States, among other countries (Mullins, 1990).
These sludges can contain high levels of heavy metals, in addition to N, P, K, and other
micronutrients. Although extensive data are available on the distribution of copper and
zinc in sludge-amended soils, the same cannot be said for such heavy metals as cadmium,
chromium, nickel, and lead. After more than 10 years of application, copper, chromium,
cadmium, and zinc have moved to the soil layer below the layer of application and zinc
has been found below the plough layer (Han et al., 2001). Zinc has been shown to be bio-
available and has been taken up by wheat, rice soybean, and maize plants. The degree of
uptake depends on the conditions of pH, soil type, and
Eh
. Heavy metals added via wastes
can runoff or seep into the soil, potentially contaminating groundwater or impacting the
quality of the food and animals within the food chain. The heavy metals may also impact
the soil microorganisms.
Heavy metals are major concerns in poultry and swine manure used as amendment to
soils. Heavy metals in poultry litter, in particular, include As, Co, Cu, Fe, Mn, Se, and Zn
(Sims and Wolf, 1994). The accumulation of heavy metals from manure amendment can
occur over the long term. Extractable Cu and Zn concentrations increase over time, in
addition to the heavy metal concentrations in runoff after amendment with poultry waste.
Cu concentrations have also increased in soil and plants such as grass and corn after the
addition of swine waste amendment (Kornegay et al., 1976; Sutton et al., 1983; Mullins et
al., 1982; Payne et al., 1988).
Although beneicial, the practice of spreading of manure can negatively impact air, soil,
and water quality. Besides providing nutrients, manure addition can reduce soil erosion
and improve soil water holding capacity (U.S. Department of Agriculture [USDA], 1992).
However, excessive levels of nitrogen, phosphorus, and organic matter can accumulate in
the soil if the manure is not spread properly (Figure 6.8).
Heavy metals such as copper and zinc may also accumulate in manure and subse-
quently in the soil due to their use as food additives. In countries such as the Netherlands,
Belgium, and Germany, 15%, 20%, and 50%, respectively, of the groundwater have nitrate
levels higher than 50 mg/L, due most likely to manure loading on the land according
to the European Commission report on the Nitrates Directive. However, EU-27 exhibited
62.5% of groundwater stations with nitrate levels less than 10 mg/L, 2.5% between 40 and
50 mg/L and 3% exceeded 50 mg/L (ec.europa.eu/environment/water/water-nitrates
/index_en.html). Large facilities, in particular, do not have suficient land to apply the
manure as a fertilizer. In the United States, it has been reported that 350 million tonnes of
manure are produced each year and that only 18% of hog farms and 23% of dairy farms
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