But pollution
also covers hundreds of chemicals which are fine or even beneficial at low levels but which if released in large quantities or in problematic circumstances cause «harm» — like
phosphorus (grows your veges but
also leads to toxic cyanobacterial blooms which kill cattle), nitrogen (grows crops kills many native species of plants and promotes weed growth costing farmers), copper (used as an oxygen carrier by gastropods but in high concentrations kills the life in sediments which feed fish), hormones like oestrogen (essential for regulating bodies but in high concentrations confuse reproductive
cycles especially with marine life) or maybe molasses from a sugar mill (good for rum but when dumped into east coast estuaries used to cause oxygen sag in estuaries leading to massive fish kills).