Real-time monitoring of pH and dissolved oxygen during disturbances in polluted sediments

Remediation activities in polluted sediments, such as dredging and capping, induce the risk of transporting polluted sediments into the water column. Turbidity surveillance is the common method for in situ environmental monitoring during such activities. However, at various stages of the remediation process, the turbidity may be caused by either clean or polluted materials. Here, the potential of using chemical sensors to discriminate between turbidity caused by clean and polluted sediments is evaluated. Dissolved oxygen (DO), turbidity and pH were measured in laboratory tests with suspensions of three different polluted sediments, as well as for two common clean capping materials. Additionally, turbidity, pH and DO were measured during dredging at one of the polluted sites. Whereas turbidity caused by clean materials did not affect pH or DO, there is an inverse linear relationship between DO and turbidity for two of the polluted sediments. Furthermore, for two of the sediments, pH is a strong indicator of sediment resuspension into the water column, with ΔpH>0.5 both in the lab and during dredging in the field. Hence, pH and/or DO surveillance is shown to be potential tools for in situ real-time monitoring of environmental risk during disturbances in polluted sediments.