The seas and oceans receive the brunt of human waste, whether it is by deliberate dumping or by natural run-off from the land.
In fact over 80% of all marine pollution comes from land-based activities and many pollutants are deposited in estuaries and coastal waters. Here the pollutants enter marine food chains, building up their concentrations until they reach toxic levels. It often takes human casualties to alert us to pollution and such was the case in Minimata Bay in Japan when many people died as a result of a pollutant building up in food chains.
A factory was discharging waste containing methyl mercury in low concentrations into the sea and as this pollutant passed through food chains it became more concentrated in the tissues of marine organisms until it reached toxic levels.
As a consequence 649 people died from eating fish and shellfish contaminated with mercury and 3500 people suffered from mercury poisoning.