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No studies on toxicokinetics of GLS exist and therefore toxicokinetic evaluation was made using constituent based approach. Majority of GLS components, hydroxides, carbonates, oxidized sulfur compounds and calcium, sodium, potassium, magnesium and manganese cations are normal and essential constituents in mammalian cells and body fluids and their concentration in the blood and tissues is strictly controlled by absorption and excretion. Therefore, under normal body physiology and handling conditions they are not likely to cause toxic effects. Carbonate and hydroxide ions in GLS could potentially affect the acid-base balance of the body. Due to their corrosive properties in high concentrations the alkalis might cause burns to the skin and therefore facilitate the exposure of GLS to the body.

GLS is rich in Ca CO3 when dry. Carbonate ions in GLS will be neutralised in the stomach due to the low pH of the gastric acid or by the bicarbonate buffer system in the blood and the interstitial fluid of vertebrates. Normal plasma concentration of carbonate as bicarbonate HCO3-is 500 -570 mg/l. The excess of HCO3-is excreted in the urine by the kidney to restore the acid-base balance. Due to the alkaline properties of carbonates irritation of the respiratory tract or skin is possible after inhalation of carbonate dust or dermal exposure. However, absorption through intact skin or through inhalation is likely to be negligible.

 

The main concerns arise from inhalation exposure of dried GLS dust. Airborne particulate matters are considered hazardous to the lungs and general health when the particles are less than five micrometres in diameter, as such particles are not filtered out by the upper respiratory tract. In high exposure concentrations impaired clearance may result in accumulation of particles in the lung (ie, lung overload). Deposition of particles onto the respiratory epithelium can lead to inflammatory response, cell injury, cell proliferation, production of reactive oxygen species, fibrosis, genotoxic effects, and even cancer. Fine and ultrafine carbon black particles have been shown to translocate beyond the lungs to other organs and particles smaller than 2.5 micrometers can cause high plaque deposits in arteries, causing cardiovascular problems. Lung diseases or conditions may influence the deposition and retention of particles. GLS dust is likely to contain at least carbon particles ofunburned coal or soot fraction of GLS. The median particle size (L50) of GLS deduced from the particle size distributions is 468.4 µm, and 10 % of the particles is under 9.1 µm. Thus GLS is not likely to be absorbed in significant amounts in the body through inhalation or deposit in the lungs under proper handling conditions. However, other elements and chemical compounds may be associated with the particulate carbon, such as toxicologically potent unsubstituted polycyclic aromatic hydrocarbons (PAHs). The amount of PAHs was not determined for this report, but according to a previous study by Enell et al. 2008, discussed in the Chapter 1.2, Composition of the substance), PAHs can be found only in trace amounts (< 0.1 %) in GLS. Nevertheless,they are likely to be tightly bound to carbon particles and not bioavailable.In addition to carbon,inorganic manganese compounds can exist in the air as aerosols or suspended particulate matter.Manganese from smaller particles(< 2.5 microns)is mainly absorbed into blood and lymph fluids, while manganese from larger particles placed in the nasal mucosa may be directly transported to the brain. Alternatively, particles deposited in the upper or lower respiratory tract may be moved by mucociliary transport to the throat and swallowed.Exposure of manganese in larger amounts or chronically, especially by inhalation, can cause neurological damage in mammals.Since manganese is eliminated from the body mainly through bile, impairments in the liver function may limit the ability of the body to excrete manganese.

Some toxicologically very potent compounds, such as sulphides, nickel, lead and cadmium can be found in GLS in trace amounts (<0.1 %) depending on the mill processes. However, since their very low concentrations in GLS their toxicokinetic characteristics are not discussed here.

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