Methods to determine the reducing capacity of dissolved organic matter in Boom Clay pore water

To study the effect of nitrate and nitrite on the reducing capacity of dissolved organic matter (DOM) in Boom Clay pore water, two methods to determine this reducing capacity have been developed and evaluated. These two methods are based on the oxidation of DOM in real Boom Clay Water (RBCW) either by ferricyanide or by ferric citrate. When ferricyanide is used as oxidant, the reducing capacity of oxidisable DOM in RBCW ranges from 3.4 to 6.1 meq/gC. For ferric citrate as oxidant, lower values of the reducing capacity of DOM in RBCW are obtained, ranging from 0.8 to 1.3 meq/gC, mainly due to its lower standard redox potential compared to ferricyanide. As these methods would be applied to investigate whether a possible redox reaction between DOM and nitrate or nitrite would cause a significant change in reducing capacity of DOM in Boom Clay, the sensitivity of both methods to nitrate and/or nitrite (and azide as microbial inhibitor) was investigated. Finally, a ‘proof of principle’ test indicated that both methods can be applied to detect changes in reducing capacity of DOM due to oxidation.