Based on this study, the heavy metal values showed mixed results. Several have exceeded the MPL, Omani Standard, for the sewage water discharge. However, there is a trend in increasing heavy metal values from the TSE to sediment, snail and grass roots. Heavy metals are the most important wastewater contaminants which cannot be removed from treated effluent. Fortunately in recent years metal production has decreased in many countries due to stringent legislations, improved cleaning technology and altered industrial activities. A significant part of the anthropogenic emissions of heavy metals ends up in wastewater. Major industrial sources include surface treatment processes with elements such as Cu, Zn, Ni and Cr as well as industrial
products that at the end of their use are discharged in wastes.