Thepopulationoftheearthisincreasingveryfast.Humansmustmaketheearthsupporttheincreasingpopulation.Thishasmadeitnecessaryforagricultureandindustrytodeveloprapidly.
Sucharapiddevelopmentproducesmoreandmorewaste,whichgoesintothewater,thesoilandtheair.Someofitismadeharmless.However,wherethereistoomuchofit,thepoisonouswastemaydogreatharmtothethingsaroundthepeople.
Whenfarmersaddfertilizertothesoiltomakeplantsgrowbetter,orusepoisontokillpests,poisonissentintotheair,thewaterandthesoil.Whenbirds,fishandpeopleeatthegrain,drinkthewaterorbreaththeair,harmwillbedonetotheirhealth.
Theairinbigcitiesisoftenmadeverydirtybycarsandfactories.Millionsoftonsofwasteandpoisonousgasesaresentintotheairwiththesmoke.Insomeplaces,littleisdonetomakethesmokecleanbeforeitgoesintotheair.
Fortunately,peoplearebeginningtorealizejusthowseriousthewholesituationis.Inmanycountries,lawshavebeenmadetostopfactoriesfromsendingoutpoisonousgases.