Many countries have been trying to prepare a regulatory limit to the use of organic wastes, such as food wastes or sludge, into crop production system in the light of their rapid increase. The regulatory system for the agricultural use of organic waste in South Korea is defined as soil concentration limits for potentially toxic elements (PTEs) to safeguard human health and crop yields. Despite legal limits, the damage of crop in the agricultural soil frequently occurs with organic waste for long-term application and with sub-quality compost made from sewage sludge.

The control system in the application of sludge to farmland varies according to country (Table 1). In South Korea, the control system for the application of sludge to farmland primarily depends upon heavy-metal concentrations that are similar to those in developed countries. Legally allowed limit values for PTEs— such as copper (Cu), zinc (Zn), chromium (Cr), cadmium (Cd), lead (Pb) and nickel (Ni) —were 400, 1,000, 250, 5, 130 and 45 mg kg-1, respectively, under the Fertilizer Management Act in South Korea (Anon., 2010a).

The control system for soil intoxication limit levels primarily depends upon heavy-metal concentration. The limit levels in South Korea are Cu 50, Zn 300, Cr 4, Cd 1.5, Pb 100 and Ni 40 mg kg-1 under the Soil Environmental Conservation Act (Anon., 2007). In Japan, Cu must be less than 125 mg kg-1, Cr 0.05 mg l-1 or less, Cd 0.4 mg kg-1 or less and Pb 0.01 mg l-1 or less (Ministry of the Environment Government of Japan, 1994).

In many countries, current rules for controlling the use of organic wastes on agricultural land have been criticized because they apparently do not take into consideration of the potential adverse effects of inorganic heavy metals and organic compounds produced in organic waste-treated soils on soil organisms (McGrath, 1994). The regulatory limit to the application of industrial waste on farmland only depends upon the level of PTEs in South Korea. However, PTEs limit may not be an adequate regulation protocol since organic wastes contain lots of inorganic and organic contaminants (Ministry of Agriculture, Fisheries and Food [MAFF], 1991).

An overall assessment of the soil contamination caused by inorganic and organic compounds of organic waste has been, therefore, attempted by ascribing qualitative description of the apparent risk and developing the integrated hazard assessment system (Hembrock-Heger, 1992). Available options for dealing with sludge include application to agricultural land, incineration, land reclamation, landfill, forestry, sea disposal and biogas. Of these, the application to agricultural land is the principal way for deriving beneficial uses of organic sludge by recycling plant nutrients and organic matter to soil for crop production (Coker et al., 1987). Also, agricultural use provides a reliable cost-effective method for sludge disposal. Recycling (81.7%) is the largest means of waste disposal, with 11.1% land deposition, 5.2% incineration and 2.0% sea disposal in South Korea (Anon., 2009). As an alternative way of waste disposal, the Fertilizer Management Act was revised to make it possible to apply industrial and municipal wastes into farmland in December 1996 in South Korea (Anon., 2006).

Table 1. Criteria of the inorganic pollutants in compost or sewage sludge for application to the arable land in 14 selected countries