Photodegradation of Australian freshwater microlayers and the implications for potable water management

Abstract

Photodegradation has been known to break down toxic compounds in potable water storages as well as degrading pesticides and herbicides in agricultural water storages. In this study, the concentration and reactivity of humic substances (HS) present in natural microlayers on water storages in South East Queensland (SEQ) was investigated. Microlayer and subsurface samples were taken from eight water storages with dissolved organic carbon (DOC) used to quantify HS concentration. The E2/E3 ratio (ratio of absorbance at 250 nm to 365 nm) was used to indicate the molecular weight of DOC compounds, and absorbance at 253.7 nm and the permanganate index were used to compare the reactivity of humified DOC. The concentration of carbonyl compounds in the microlayer was also investigated as carbonyls are considered the most photoreactive functional group present in HS. Preliminary results indicate that the concentration of humic substances and their chemical reactivity in SEQ water storages are highly variable, reflecting the characteristics of the water catchments.