Chemistry Of Water Pollution

1. Introductionwaterthechemistryof waterpollutionMaking the case: Water of life2. Sources of water pollution3. Main pollutants4. Eutrophication5. Bioaccumulation and biomagnification6. Endocrine disruptors7. Oil spills

IntroductionWater (H2O) is an essentialchemical for life on Earth1Making the case: Water of lifeThe quality of water can be dramatically affected bypollution. Water pollution is caused by foreign objects andchemicals entering the aquatic ecosystem or when naturalchemicals build up in excess amounts.There are two types of water pollution:Point Source – when pollutants enter the water course at specificsites, such as a discharge pipe.Diffuse – when there isn’t an obvious source of pollutionand it occurs over a wide area. Examples include run-offfrom agricultural land and urban areas. This type ofpollution can be difficult to identify and control.In Scotland, diffuse pollution is the largestpollution pressure on the waterenvironment.

Water sampling, mine water treatment schemeSources of water pollutionAmmoniaPollution to the water environment can comefrom a wide range of sources. These include:Agriculture (crops and livestock)Atmosphere (acid rain)AquacultureForestryIllegal dumping of wasteIndustryMinesSewageUrban areas and roads2Making the case: Water of hosphateNH4SulphurSSulphateSO24

Main pollutantsToxic metalsAmmonia (NH3)/Ammonium (NH4)Nitrate (NO3)/Nitrite (NO2)(Agriculture, aquaculture, industry, urban)Ammonia is highly toxic to fish and can convert intonitrates.(Agriculture, industry, aquaculture, sewage)These can accelerate aquatic plant growth leading toeutrophication.(Mining, urban, industry)These include arsenic (As), mercury (Hg), selenium (Se)and lead (Pb) and can persist in the environment fordecades. They can be poisonous to aquatic life and mayslow down their development.Crude oil (Hydrocarbons (HxCx))Phosphorous (P)/Phosphate (PO43-)(Urban, industry)This mainly enters the marine environment in oil spillsand can have detrimental effects on marine animals,plants and birds.(Agriculture, urban)Similar in effect to nitrates, these can also lead toeutrophication of water bodies.Sulphates/sulphide minerals(minerals containing S2-)Mine water treatment scheme3Making the case: Water of life(Mining)Sulphur dioxide mixes with water particle in the air to formacid. This falls as acid rain leading to acidification of waterbodies. Sulphide minerals can be unearthed during themining process and are a leading cause of acidification ofwater in mines. When this acidic water is discharged it isknown as acid rock drainage. The most common mineralassociated with this process is pyrite (FeS2).

EutrophicationEutrophication is the process throughwhich a body of water becomesenriched with chemicals such asnitrates and phosphates. Algae andother aquatic plants then feed on thesenutrients leading to excess growth.This leads to a reduction in the amountof dissolved oxygen available as algalblooms on the surface restrict theamount of sunlight penetrating thewater limiting photosynthesis whichcauses the death and decomposition of plantlife underwater. The lack of dissolvedoxygen also kills all animal life inthe water body.Eutrophication surveyExample ofa phosphatemolecular model4Example of a nitratemolecular modelMaking the case: Water of lifeAlgal blooms

Bioaccumulation and biomagnificationBioaccumulation is the build-up of toxic substances ina food chain. A common example in aquatic systemsis the accumulation of heavy metals such as mercury(Hg) in fish.At the start of the chain, mercury is absorbed byalgae in the form of methylmercury (CH3Hg ).Fish then eat the algae and absorb the methylmercuryand since they are absorbing it at a faster rate than it canbe excreted, it accumulates in the body of the fish.Further up the food chain, predatory fish and birdsthen absorb the mercury from the fish theyconsume, which then accumulates in their bodiesleading to a higher concentration of the mercury intheir own bodies than in the species they have eaten.This is known as biomagnification. This process canbe dangerous to humans as we could consumefish which have bioaccumulated mercury andabsorb it ourselves, causing health problemssuch as damage to the centralnervous system.5Making the case: Water of life

Endocrine disruptorsEndocrine disrupting compounds (EDCs)are chemicals which can interfere withthe normal function of hormones in aquaticanimals. They can enter water coursesthrough wastewater discharges from industryand sewage and also in agriculturalrun-off. Common EDCs entering the waterenvironment are tributyltin which waswidely used in anti-fouling paint on ships’hulls and phthalate esters which aremainly used in plastics. They are known toimpair growth and development inthe animals, lead to reproductiveabnormalities and can even causesome species to change sex.Arctic SkuaFreshly caughtcodExample of a Triclosan antibacterial molecular model6Making the case: Water of lifePollution from concrete waste pipe

Oil spillsDead fishFish larvaeWhen an oil spill occurs it can cause a lot of harm to all life in thearea. It destroys the insulating ability of fur in mammals such assea otters and the water repelling properties of birds’ feathers.This means they are more exposed to the elements which canlead to hypothermia and death. Recently, it has also been shownthat polycyclic aromatic hydrocarbons in oil can cause fish tohave heart attacks and in lower concentrations disrupt thedevelopment of fish larvae.Bird killed in oil spillCrab in crude oil spill7Making the case: Water of life

Diffuse - when there isn't an obvious source of pollution and it occurs over a wide area. Examples include run-off from agricultural land and urban areas. This type of pollution can be difficult to identify and control. In Scotland, diffuse pollution is the largest pollution pressure on the water environment. 1 Making the case: Water of life