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Estuaries in NSW

Estuarine Water Quality

Methylene Blue Active Substances

Detergents such as washing powders and liquids contain surfactants whose purpose is to facilitate the "wetting" of items being washed. This enables the detergent itself to work more effectively in cleaning the item. The level of surfactants (and hence detergents) in water can be determined by measuring the amount of methylene blue active substance (MBAS).

Detergents have a range of ill-effects on aquatic organisms. Detergents are organic compounds, and as such can cause significant oxygen demands within a waterbody, resulting in depressed DO levels and attendant detrimental effects. Early detergents contained high levels of phosphates, an aquatic nutrient (modern detergents contain much lower levels). The surfactant effect of detergents can destroy natural water-repellent oil layers on animals, thereby wetting surfaces which are normally dry. This can facilitate attack by parasites, and in the case of aquatic plants, loss of control over gas and water exchange through surface tissues and subsequent death. In fishes, detergents cause strong sliming of gills and disrupt their sense of balance. Fish are often killed as a result of exposure to high concentrations of detergents.

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