There are many different chemicals in the form of pollutants, and they range from simple ions to complex molecules. These pollutants make up different classes, and each class have unique properties.
Organic pollutants are ones that usually contain carbon. Many of these are remains of living organisms. Some examples of these organic pollutants are hydrocarbons, PCBs, insecticides and detergents. Hydrocarbons are further divided into two classes: 1. single-bonded alkanes, double-bonded alkenes, and triple-bonded alkenes and 2. aromatic hydrocarbons containing ring structures and are also more reactive than the first class. PCBs are stable unreactive fluids used for hydraulic fluids, coolant/insulation fluids in transformers and plasticizers in paints. PCBs are also not water-soluble, and banned in some countries. Insecticides such as DDT's are harmful in the sense that the fat tissues of lower animals they accumulate enter the food chain, and have been banned decades before.
Inorganic fertilizers are not necessarily toxic, but can become a threat to environment when improperly used. Nitrates and phosphates are main components of fertilizers, and these compounds cause algal blooms in surface water. This results a decline in oxygen level of the water, and thus create eutrophication. This process involves the uptake of oxygen by microrganisms that break down algae resulting in oxygen starvation.
Metals are good conductors of electricity and generally enter chemical reactions as cations - positive ions. These metals are natural substances from weathering of ore bodies sometimes relocating to places where they can cause massive environmental damage. Found in surface waters in their stable ionic form, some examples of harmful metals are lead, zink, manganese, calcium and potassium. Their reactions to other ions makes them a pollutant, which involves electron transfer reactions with oxygen. This leads to formation of toxic oxyradicals. Also, some metals can become metalloids and then bond to organic compounds to form lipophilic substances that are highly toxic. These poisons can be stored in the fat-suplly of animals and humans. Having a desnity of greater than five which is also the root of its name, heavy metals are the most dangerous metals. Because they cannot be broken down into smaller and less harmful parts, they are non-biodegradable meaning the only possible workaround is if the metal is stored in body tissues.
Pollutants can enter the environment in a number of ways, but they are mostly from the discharge of sewage water which is very harmful, especially when the waste - usually industrial in nature - is released directly unto surface water. Domestic sewage water are composed mostly of paper, soap, urine, feces, and detergents while industrial wastes range depending on the specific procesess it underwent. Heavy metals enter through mining and smelting operations, chlorphenols and fungicids with pulp mills, insecticides with mothproofing factories. Land pollution is easier to control than water, because activities like offshore oil and manganese extraction are more difficult to monitor. That said, oil, through oil tankers and shipwrecks are released into bodies of water, usually the seas. Paints on boats decays in time, and in long trips on the ocean which eventually gets stuck at sea. Pesticides, on the other hand, are applied to water for aquatic pest control. Compounds such as nitrates and phosphates are absorbed by plants, and in their death, they are released into the soil, which gets washed away out of shore. Aside from those, another way pollutants can enter is accidentally by atmospheric deposition. This way, chemicals enter the water easily, because they are converted in the form of droplets or sprays.
The effect of these pollutants can be largely seen in small inland seas and lakes because larger bodies of water have natural dilution systems for incoming pollutant whereas the the smaller ones do not.
These pollutants can affect living things in a variety of ways sometimes positively while others not. When a pollutant first enters the body, one of the initial reactions is setting up protective mechanisms - for example detoxification, - but these types of defense sometimes produce substances that causes more harm to the cells than the actual pollutant. A different response is reducing the availability of pollutants through chemical reactions, to either excrete of store them. Even moreso, an organism can produce substances that repairs these type of damages, but the response to toxicity is largely depended on the amount of pollutant ingested, and the quality of the repair tissues of the organism. When these mechanisms fail, the pollutants then completely cause complications. Genotoxins are compounds that enter the body and damages DNA. This genotoxins are the cause for the formation of mutant cells that produce defects, oftentimes hazardous to health. Sometimes the effect is carcinogenic which is cancer inducing. Other times, the complication is neurotoxic which have neurological effects on the organism. Lastly, pollutants can cause reproductive failures. These are called endoctrine disruptors.