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Environmental fate & pathways

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As an inorganic compound, traditional degradation studies are not applicable to STPP. The degradation pathway is through hydrolysis to pyrophosphate with further hydrolysis to orthophosphate

An additional environmental issue concerning phosphates in general, and therefore also STPP, is their role in the nutrient enrichment of surface waters (eutrophication).

STPP is hydrolysed in the sewerage pipes, the sewage treatment plants and the environment to soluble inorganic phosphates (orthophosphate PO43-) or transformed to insoluble inorganic forms. These are the same phosphates as those formed by natural hydrolysis of human urine and faeces, animal wastes, food and organic wastes, mineral fertilisers, bacterial recycling of organic materials in ecosystems, etc. These phosphate forms are bio-assimilated by the bacterial populations and the aquatic plants and algae found in these different compartments.

Phosphates are an essential nutrient (food element) for plants, and stimulate the growth of water plants (macrophytes) and/or algae (phytoplankton) if they represent the growth-limiting factor. Although in some cases nutrient enrichment will be absorbed and might not have an apparent effect, in other circumstances, it can lead to negative effects. These can range from ecosystem modifications, through algal blooms, to in extreme cases (through decomposition of plant biomass) oxygen depletion and collapse of the biocenosis in a surface water.

De Madariaga BM (2007) developed a conceptual model and protocol for performing European quantitative eutrophication risk assessments of polyphosphates in detergents. In this model, the risk probability for eutrophication occurring in the most sensitive areas of a river basin (lakes, reservoirs, meadow zones, estuaries), is based on the TP (total phosphorous) concentration of the inflow water. The variability observed for similar TP concentrations is the consequence of variations in concentrations of N and/or other nutrients, other ecosystem factors and other natural variability.

The study also covered the implementation of the model and a set of examples based on generic European scenarios as well as a pan European probabilistic estimation covering the diversity observed for the European conditions and enabled a probabilistic risk assessment of eutrophication relating to the use of STTP in detergents.

The scientific validity of this methodology was confirmed by the EU scientific committee SCHER (Opinion of 29th November 2007).

Heavy metal mobilisation:

Studies on the effects of STPP indicate that although complexation can occur between heavy metals and STPP, there is generally little effect on the rate of uptake by aquatic organisms and no significant differences in heavy metal concentrations in aquatic systems were found (Barica et al, 1973).

In studies with mammals orally dosed with cadmium, reductions in toxicity were observed when STPP was administered at the same time compared to dosing with cadmium alone, indicating that there is a reduction in heavy metal bioavalibility when administered with STPP (Andersen et al, 1988 and Engström et al, 1984).

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