The product from the burning of a combination of carbonaceous materials.

Endpoint summary

Additional information

The Ash is a mixture of many compounds, majority of which are inorganic materials. The main components of the Ash are calcium, silicon, iron, magnesium, phosphorous, potassium, sodium and aluminum with the remainder of the material being a variety of other chemical identities. For risk assessment purposes, critical components of Ash were selected for further research based on the following criteria; 1) they were found to be bioavailable based on an acetate leaching test (> 20 % of the total concentration was extractable in acetate), 2) their concentrations in Ash exceeded the guidance limits set by Finnish authorities for contaminated soils, and 3) their bioavailable concentrations in Ash exceeded the Total Daily Intake (TDI). The critical components were arsenic, barium, cadmium, copper, lead and antimony. Also, aluminum, the only non-essential element among the main components of Ash, was selected for further chemical risk assessment.

Ash as a physical compound is highly insoluble in water. Some components, however, may leach from ash in a long run. Acetate leaching test is used for determining so called "exchangeable metal fraction", which includes weakly adsorbed metals retained on the solid surface by relatively weak electrostatic interaction, metals that can be released by ion-exchange processes and metals that can be co-precipitated with carbonates present in many types of sediment (Filgueiras et al, 2002). Exchangeable fraction of metals is susceptible for being mobilized or taken up by biota.

Mobility and consequent distribution of metals is dependent on their speciation in the ambient environmental conditions. Arsenic is relatively mobile at the pH values typically found in environment (6.5-8.5) and over a wide range of redox conditions. Arsenic is deposited on sediments mainly by binding or co-precipitating with metal oxides of Fe, Al and Mn. If conditions in sediments become anoxic, metal oxides dissolve releasing arsenic. In reducing conditions As prevails in solution in trivalent i.e. more toxic form. However, if high concentrations of free sulfides are present, then arsenic can be precipitated as sulphide minerals (Cullen and Reimer, 1989, Guo et al., 1997). Cadmium occurs as cation Cd2+ in solution but at near-neutral pH solubility becomes limited by precipitation or co-precipitation with other metals. Under oxidizing conditions, a part of Cd prevails in solution. Under anoxic conditions, Cd tends to bind to carbonates or sulphides (Guo et al., 1997). Antimony adsorbs onto suspended particulate material (mainly onto Fe oxides) and adsorption is enhanced at low (< 5) pH conditions, and in the anoxic base of stratified lakes (Wilson and Webster-Brown, 2009). Sedimentary sulfides and organic carbon form important binding phases for copper and lead (Mahony et al., 1996). In addition, copper also has a high affinity to dissolved organic carbon and in water phase only a small fraction of copper (< 1%) exists as free ions (Achterberg et al., 2002;Temminghoff et al., 1997). Aluminum is highly soluble at low (<6.0) and high (> 9.0) pH, but very insoluble in near-neutral water due to hydrolysis and formation of Al(OH)3, high reactivity of Al hydroxide polymers with insoluble organic and inorganic ligands and strong binding to particulate matter (Driscoll and Schecher, 1990; Xu et al., 2002).

 

In conclusion, the critical components of Ash tend to be tightly sorbed on solids in most prevailing environmental conditions making them less bioavailable to biota.

The critical components of Ash (As, Ba, Cd, Cu, Pb, Sb) were found to bioaccumulate in organisms living in the contaminated environment. However, bioconcentration factor calculated as an average of all species and trace elements was 107 indicating that in general bioconcentration of ash-related trace elements is low. Bioaccumulation has been found dependend on the species with the predators having lowest body burdens (Culioli et al., 2009). Bioaccumulation has been generally found to be inversely dependent on metal concentration (DeForest et al., 2007).

Biodegradation and hydrolysis are not relevant for inorganic substances.

 

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Guo T., DeLaune R. D. and Patrick Jr. W. H., The influence of sediment redox chemistry on chemically active forms of arsenic, cadmium, chromium, and zinc in estuarine sediment, 1997, Environment International 23(3), 305-316.

 

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Temminghoff EJM, van der Zee SEATM, de Haan FAM, 1997, Copper mobility in a copper-contaminated sandy soil as affected by pH and solid and dissolved organic matter, Environ. Sci. Technol. 31, 1109-1115.

 

Wilson N, Webster-Brown J, The fate of antimony in a major lowland river system, the Waikato River, New Zealand, 2009, Applied Geochemistry 24, 2283–2292