Sacrificial anodes attached to the hulls of boats and marine structures to prevent corrosion. Their use inevitably leads to significant loads of zinc as well as impurities such as cadmium being released into the saline environment. Risk assessments and source apportionment exercises require accurate assessments of the potential loads of chemicals into the environment. This research has surveyed a wide variety of zinc anodes for their composition to compare against reported industry standards as well as using a number of contrasting methodologies to determine the dissolution rate of zinc from anodes into water. Based on the varying methodologies presented here, it is proposed that risk assessments and source apportionment exercises use a zinc dissolution rate of 477 g/yr/kg of anode. This is the mean value for all survey data from 131 boat owners across the UK and equates to between 1.9 and 2.9 kg of zinc per vessel being dissolved from anodes per year depending on whether the median or mean number of anodes per vessel are used respectively. Data suggested greater rates of zinc dissolution at higher salinity. Although most anodes tested had concentrations of cadmium within the proscribed limits set by the US Military, calculated leaching rates from laboratory dissolution experiments suggested that between 53 and 405 kg per year of cadmium is leached into the saline environment from the use of zinc anodes. It was therefore concluded that given cadmium is a priority hazardous pollutant, then its content in zinc anodes should be minimised where ever possible.
|Journal||Marine Pollution Bulletin|
|Publication status||In preparation - Jan 2020|