The main effects of nitrate pollution are
Children below the age of sixth months have insufficient acid in their stomachs to kill bacteria effectively. Under certain conditions, bacteria can grow that are capable of reducing nitrate(V) ions to nitrate(III) ions.
Nitrate(III) ions (also called nitrite ions) can convert the iron(II) in haemoglobin to iron(III) which prevents haemoglobin from transporting oxygen.
This condition is known as methaemoglobinaemia or 'blue baby' syndrome.