PERSONALISIMA

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volume of solid waste generated (Turan et al. 2009; Wong et al. 2006). The common methods of solid waste disposal are open site dumping, landfills and incineration (Kinnaman 2009; Turan et al. 2009). The most economical and common method of solid waste disposal in many countries is either burial in landfills, or incorporation into sea-fills (Khoury et al. 2000; Kjeldsen et al. 2002). Studies on coastal fill and sea- fill activities have shown that high levels of trace elements can be released into the surrounding marine environment from the fill materials (Chifamba 2007; Jones 2010). Therefore, improper management of solid waste can cause serious environmental and health consequences, due to the risks associated with leaching of contaminants, including trace elements from waste disposal sites (Christensen et al. 1994; Jones 2010; Kjeldsen et al. 2002).

1.3.1 SOURCES OF TRACE ELEMENTS IN FILL MATERIALS

Sources of trace elements in MSW include batteries, consumer electronics, ceramics, light bulbs, house dust and paint chips, lead foils, used motor oils, plastics, inks and glass (Whittle & Dyson 2002). Sources of arsenic in MSW are wood preservatives, paints, dyes, ceramics, glass, electronics, pigments, and antifouling agents (Akter et al. 2005; Leonard 1991). The primary source of cadmium in MSW is rechargeable nickel-cadmium batteries and some plastic materials, while lead comes from variety of sources like plastics, road dust and paint chips (Heck et al. 1994). The main contributors of mercury to MSW are used household batteries, broken thermometers, and fluorescent lamps (Heck et al. 1994). Sources of copper, iron and zinc in MSW include electric wiring materials, galvanised materials, scrap metals, cooking pots, kitchen wares, plastic materials, treated woods and cardboards, paper material, and food tins and containers (Chifamba 2007; Long et al. 2011).

Sources of trace elements in fill sites considered to contain clean materials (i.e. building materials), such as the one in Lyttelton Harbour, include treated timbers, concrete reinforced metal bars, paint chips, plastics, electrical ducting, elemental copper in the form of cabling, cable sheathing and panel products (LPC 2011; Sneddon 2011). These materials may be inadvertently incorporated in fill materials, and are known to release trace elements to the surrounding environment (Akter et al. 2005; Denton et al. 1997; Heck et al. 1994; Leonard 1991).

1.3.2 LEACHATE GENERATION FROM FILL ACTIVITIES

In landfills, leachate is generated as rainwater passes through the layers of the landfill, acting to transfer the pollutants into the percolating water (Ettler et al. 2008; Kjeldsen et al. 2002). Marine landfills or sea-fills are subjected to similar processes via seawater percolation (Kjeldsen et al. 2002). When seawater levels rise and fall with the tide, seawater penetrates through the layers of wastes creating leachate (Jones 2010). Studies on leaching from fill activities near coastal sites and sea-fill have reported that contaminant levels in seawater around the dump site were higher than the levels found in waters more distant from the waste site (Jones 2010; Maata & Singh 2008; Naidu & Morrison 1994).

Solid wastes in fill activities undergo physical, chemical and biological degradation processes as the refuse decomposes (Kjeldsen et al. 2002; Taulis 2005). The concentration and composition of leachates may differ depending on the waste type in the fill, and the decomposing environmental conditions (i.e. aerobic or anaerobic) (Kjeldsen et al. 2002). There are four distinctive stages of refuse decomposition in terrestrial landfills. These are the aerobic phase, the anaerobic acid phase, the initial methanogenic phase, and the stable methanogenic phase (Farquhar & Rovers 1973; Kjeldsen et al. 2002). When the decomposing condition is aerobic, a number of biological and chemical reactions can occur leading to the anaerobic acid phase, where lowering of pH occurs, increasing the oxidation-reduction potential, and increasing the cation exchange capacity of the refuse (Kjeldsen et al. 2002). The increase in oxidation-reduction potential can increase the formation of oxidised functional groups such as carboxylic acids on humic matter (Kjeldsen et al. 2002). These alterations in the refuse decomposition process can result in an overall increase in trace element mobilisation, and increased concentrations of trace elements in the leachate (Khoury et al. 2000; Kjeldsen et al. 2002). Little work appears to have been carried out to establish whether the characteristics of terrestrial fills are also present in marine fills.

Leachates contain a complex mixture of contaminants, and the broader categories of contaminants in leachate include dissolved organic matter, inorganic macrocomponents, trace elements and xenobiotic organic compounds (Christensen et al. 1994; Jones 2010; Kjeldsen et al. 2002). Dissolved organic matter includes

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components such as volatile fatty acids and fulvic-like and humic-like compounds. Inorganic macrocomponents include calcium, magnesium, sodium, potassium, ammonium, chloride, sulphates, and hydrogen carbonates. Xenobiotic organic compounds include a variety of aromatic hydrocarbons, phenols, chlorinated aliphatics, pesticides, and plasticisers. Trace elements present in leachates include arsenic, cadmium, chromium, cobalt, copper, lead, mercury, nickel and zinc (Kjeldsen et al. 2002). A wide variation in trace element concentrations has been reported for different landfill sites (Table 1.1) (Kjeldsen et al. 2002).

Table 1.1: Range of trace element concentrations in various landfill leachates

Trace element Concentration in landfill leachate ( µg L-1)

Arsenic 10 - 1000 Cadmium 0.1 - 400 Copper 5 - 10000 Iron 3000 - 5500000 Mercury 0.05 - 160 Lead 1 - 5000 Zinc 30 - 1000000

Adapted from Kjeldsen et al. (2002)

Trace elements deposited in fill activities can be released from the fill materials, a process that may take decades (Flyhammar 1995; Kjeldsen et al. 2002). However, there are processes that will also act to slow leaching. For example, Belevi & Baccini (1989) and Bozkurt et al. (2000) predicted that trace elements can be immobilised for hundreds of years by the alkaline conditions generated by the stable phase of decomposition. Sorption to organic matter and soil, and precipitation are also thought to play a significant role in immobilising trace elements in refuse (Kjeldsen et al. 2002). In addition, sulphides (formed by reduction of sulphates under the alkaline conditions generated at the stable methanogenic phase) can immobilise trace elements by formation of insoluble metal sulphides, which explains the low concentration of trace elements measured in some leachates (Christensen et al. 1994).