ALIMENTOS DEFINITIVOS, TEMPORALES Y PROVISIONALES

SOURCES

OF

CONTAMINATION

TO

THE

MARINE ENVIRONMENT

The main focus of this thesis was to investigate four toxic trace elements: arsenic, cadmium, mercury and lead. However, nutrient trace elements such as copper, iron and zinc, are also prominent in aquatic settings and can also produce toxic effects at higher concentrations. Therefore, these essential elements were also investigated in this study along with the non-essential elements.

1.2.1 ARSENIC

Although arsenic is in group five, and is thus classified as a non-metal in the periodic table, it is often referred to as a metalloid, because it shares similar physical and chemical properties with both metals and non-metals (Akter et al. 2005; Rainbow et al. 2006a). Arsenic can be found in the natural environment in both organic and inorganic forms, and in several oxidation states (-3, 0, +3 and +5) (Akter et al. 2005; Eisler 1988; Smedley & Kinniburgh 2002). In natural waters it is mostly found as inorganic arsenite [As3+] or pentavalent arsenate [As5+] (Smedley & Kinniburgh 2002). As3+ is more toxic than As5+, which in turn is more toxic than methylated or organic arsenic species (Sharma & Sohn 2009; Smedley & Kinniburgh 2002; WHO 2001). It is the less toxic organic arsenic species such as arsenobetaine and arsenosugars that are the predominant forms found in marine organisms (Francesconi & Edmonds 1998; Neff 1997).

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enamels (Denton et al. 1997). The anthropogenic sources of arsenic to the marine environment include agricultural runoff from use of fertilisers and pesticides, urban runoff, industrial waste, treated woods and timbers, and municipal solid wastes. Toxicity associated with arsenic exposure can lead to a range of diseases such as skin disorders, lung diseases, liver diseases, peripheral vascular disease, hypertension, heart disease, and cancer of skin, lung and urinary bladder (Fatmi et al. 2009; Graeme & Pollack 1998; Mazumder 2008).

1.2.2 CADMIUM

Although cadmium and zinc are placed in the same group in the periodic table, cadmium is considered a non-essential element while zinc is classified as an essential element. Cadmium is able to displace zinc from zinc-containing enzymes (O'Neill 1998) and can therefore inhibit the essential roles of these enzymes in the body. Although the chemical properties of cadmium and zinc are very similar, the hydrated zinc ion (Zn2+) is relatively more stable than the hydrated form of cadmium ion (Cd2+) in aqueous form (O'Neill 1998). Cadmium is able to compete (i.e. bind) more strongly than zinc for binding sites, and thus is favoured in terms of formation of metal- sulphur bonds (O'Neill 1998).

The general uses of cadmium include electroplating, plastic stabilisers, pigments, plastics, glass, ceramics, semiconductors, and in nickel-cadmium batteries (Hutton 1983; O'Neill 1998). The major anthropogenic sources of cadmium to the environment are the steel industry, waste incineration, mining activities, agricultural runoff from use of phosphate fertilisers, and zinc production (GESAMP 1985; Hutton 1983). The toxic effects of cadmium include kidney failure, itai-itai disease, disruption of enzymatic pathways, anaemia, liver disorders, weakening of bones that can lead to osteoporosis as seen in itai-itai disease (which also requires a low calcium intake), and lung cancers (Finkelman 2005; GESAMP 1985).

1.2.3 ZINC

The major uses of zinc include zinc-based alloys, brass and bronze, galvanising works, paints, manufacturing of batteries and rubber materials as well as in sacrificial anodes on marine water craft (Denton et al. 1997). The sources of zinc to the marine environment include storm water discharge, burning of fossil fuels, municipal solid

wastes, brass and galvanised fittings on boats, zinc-based anti-corrosion and anti- fouling paints on boats, and from applications of fertiliser and pesticides near coastal areas (Denton et al. 1997). Although zinc is an essential element, excess intake can disrupt essential enzymatic functions in both humans and aquatic organisms (Berthet et al. 2003; O'Neill 1998; Rainbow 2007).

1.2.4 LEAD

Lead is one of the few trace elements that can be found in its metallic form in nature, but more frequently lead is present in its +2 oxidation state (O'Neill 1998). Organolead compounds, particularly alkyl-lead forms, are considered more toxic than other species of lead (O'Neill 1998). Lead in the marine environment can precipitate as lead sulphide, an insoluble compound, and often exists as forms with low bioavailability such as bound to suspended sediment particulate matter (O'Neill 1998). These forms of lead can be remobilised by changing environmental conditions, such as a reduction in pH (Kjeldsen et al. 2002). Approximately 5% of the lead in aquatic systems is in the dissolved form (O'Neill 1998). Like most trace elements, lead has a high affinity for thiol (-SH) groups in biological molecules and can strongly bind proteins, and also nucleic acids (O'Neill 1998).

The key uses of lead are in lead-acid storage batteries in motor vehicles, lead alkyl compounds that are added to petrol to reduce knock in combustion engines, as electrodes in electrolysis, in pigments, lead paints, solder, anti-fouling paints and as stabilisers in plastics (Chen et al. 2005; Denton et al. 1997; Järup 2003; O'Neill 1998; Wu et al. 2000). The anthropogenic sources of lead to the marine environment include discharge from manufacturing processes such as metal processing works, discharge from mining activities, combustion of leaded fuels, burning of wood and coals, solid waste incineration, atmospheric deposition, domestic wastewater and sewage wastes (Cabral-Oliveira et al. 2015; GESAMP 1985). Lead toxicity can manifest as a wide range of impacts such as impairment of blood synthesis, hypertension, hyperactivity, bone defects, weakness in fingers, wrists and ankles, miscarriage in pregnant woman, and brain damage (D'Souza et al. 2003; Finkelman 2005; GESAMP 1985; O'Neill 1998).

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1.2.5 MERCURY

Mercury is the only metal that is liquid at room temperature, and it is very volatile in air. Most compounds of mercury are also volatile (Gochfeld 2003; O'Neill 1998). Mercury exists in the 0, +1, +2 oxidation states and methylation is a very important feature of mercury cycling in the aquatic environment. The main form of mercury found in fish is methylmercury, which generally accounts for over 90% of total mercury (Hight & Cheng 2006; Olmedo et al. 2013). Mercury entering aquatic systems will be methylated by microorganisms and abiotic processes and converted to methylmercury, a form that has high bioavailability, and which biomagnifies through food chains (Gochfeld 2003; O'Neill 1998). This is also a form of mercury that is higher in toxicity than inorganic species (Gochfeld 2003; Monperrus et al. 2007). Under alkaline conditions, sulphide ions (S2-) can turn soluble mercury compounds into insoluble mercury (II) sulphide, and when the pH of the system decreases, it favours solubilisation, and hence greater potential for the synthesis of methylmercury by microorganisms (Gochfeld 2003; O'Neill 1998).

Mercury is used in the production of chlorine and acetaldehyde, electrical equipment, instruments such as thermometers, as a catalyst in the production of plastics, in pesticides, as a preservative in vaccines, in pharmaceuticals, in the dental industry and as a component of anti-fouling paints (Denton et al. 1997; Fimreite 1970; Gochfeld 2003). Sources of mercury to the marine environment include coastal or sea-fill activities, industrial waste, discharge from mining activities, sewage outfalls and atmospheric deposition (Heck et al. 1994; Wuana & Okieimen 2011). Mercury toxicity includes severe kidney damage, neurological disruption, and behavioural disturbances (Langford & Ferner 1999).

1.2.6 COPPER

Copper is an essential trace elements that is moderately abundant in the natural environment. Copper presents in the aquatic environment primarily in the +2 oxidation state (e.g. CuOH+, CuCO3, CuSO4), but also in the cuprous form (Cu+ which rapidly becomes Cu2+ in the aquatic environment) (Callender 2003). Copper is known to have high affinity for clay mineral fractions, especially organic carbon and manganese oxides, and concentrations of copper in the aquatic environment are

strongly dependent on the type and concentration of inorganic and organic ligands present (Callender 2003). In this regard, numerous studies have demonstrated that aquatic copper toxicity can vary depending on the type of complexing ligand and the concentration of cations that may compete with copper for binding sites and uptake pathways (McGeer et al. 2002; Paquin et al. 2002; Santore et al. 2001).

Copper is used in the electrical industry, as a catalyst in alloy form, as a wood preservatives, in pesticides, and as a component of anti-fouling paints (Denton et al. 1997; Santore et al. 2001). Sources of copper to the marine environment include discharge from mining and smelting activities, domestic and industrial wastewaters, steam electrical production, MSW disposal at coastal sites, incineration emissions, sewage outfalls, antifouling paints, wood preservatives, port operation activities, and urban stormwater runoff (Denton et al. 1997; Jones 2010; O'Neill 1998; Williamson et al. 2003). Although copper is an essential element in several enzymes and is involved in the synthesis of haemoglobin, excess exposure to copper can result in various toxic effects in humans including irritations in nose, mouth, and eyes, severe headaches, dizziness, nausea, and diarrhoea (Finkelman 2005).

1.2.7 IRON

Iron is an essential element found in various oxide forms, and often presents in the environment as divalent iron (Fe2+) and trivalent iron (Fe3+) compounds. Iron is not often considered a toxic trace element in the environment, and it is usually found at high levels in both marine sediments (Jones 2010; Turner 2000), and biota (Brooks & Rumsey 1974; Kennedy 1986; Turoczy et al. 2001). Uses of iron are numerous, and include utility as a construction material in ships, heavy vehicles and buildings, and as piling materials in wharfs and seawalls. Anthropogenic sources of iron to the marine environment include industrial discharge, stormwater runoff, acid mine drainage, port operation works, ship hulls, wharves, and coastal fill sites (ECan 2008; Jones 2010; Winterbourn et al. 2000).