Young-Eun Na1, Hea-Son Bang1, Soon-Il Kim2 and Young-Joon Ahn2 1National Academy of Agricultural Science and Technology, Rural Development Administration, Suwon 441-707, 2WCU Biomodulation Major, Department of Agricultural Biotechnology,

Seoul National University, Seoul 151-921, Republic of Korea

1. Introduction

Earthworm populations show a considerable amount of variability in time and space, with mean densities and biomass ranging from less than 10 individuals and 1 g m-2 to more than 1,000 individuals and 200 g m-2 under favourable conditions. Earthworms have been considered to play a great role in soil-formation processes and in monitoring soil structure and fertility (Lavelle & Spain, 2001) because they may increase the mineralisation and humification of organic matter by food consumption, respiration and gut passage (Edwards & Fletcher, 1988; Lavelle & Spain, 2001) and may indirectly stimulate microbial mass and activity as well as the mobilisation of nutrients by increasing the surface area of organic compounds and by their casting activity (Emmerling & Paulsch, 2001). However, within particular climatic zones, earthworm assemblages, with fairly characteristic species richness, composition, abundance and biomass, can often be recognised in broadly different habitat types, such as coniferous forest, deciduous woodland, grassland and arable land (Curry, 1998).

Agriculture is facing a challenge to develop strategies for sustainability that can conserve non­renewable natural resources, such as soil, and enhance the use of renewable resources, such as organic wastes. It has been estimated that 357,861 tons of organic sludge daily were produced in South Korea in 2009 (Anon., 2009). The production and use of organic compounds have also risen rapidly over the last four decades. Organic compounds which are released either through direct discharge into the sewer system, or indirectly through run-off from roads and other surfaces are found in sewage sludge (Halsall et al., 1993). As a suitable bioindicator of chemical contamination in soil, earthworms are easy, fast and economical merits to handle. Especially, analysis of their tissues may also provide an excellent index of bioavailability of heavey metals in soils (Helmke et al., 1979; Pearson et al., 2000).

Although the acute earthworm toxicity test developed by Edwards (1984) has been widely used and an internationally accepted protocol was also used for assaying the chemical toxicity of contaminants in soils (Organisation for Economic Cooperation and Development [OECD], 1984), the chronic toxicity test to detect subtle effects of contaminants on them by long-term exposure has not been fully achieved (Venables et al., 1992). Based upon these tests, lots of information on heavy metal uptake, toxicity and accumulation by various

earthworm species have been produced. Therefore, earthworms could fill the gap by being used as potential biomarkers of ecotoxicity to various chemicals, including organic contaminants.

This chapter is particularly focused on the hazardous effects on composition, numbers and biomass of Megascolecid and Moniligastrid earthworms, which are dominant groups in South Korea, of 8 consecutive yearly applications of three levels of four different organic sludges and pig manure compost as a positive reference using field lysimeters and microcosms.