The pollution levels in rainwater are made up of a number of
pollutants, inorganic pollutants, metals, organic pollutants and microbial
pollutants (Meric, 2016).
Rainwater is the purest water found naturally, and contains a wide range of
ions and cations (N.F.Gray, 2008)
When speaking about inorganic pollutants the main issues are
pH and minerals, the mean pH of rainwater is in the acidic range. The acidity
of rainwater naturally is taken as 5.6 (Meric, 2016).
At a pH level of 6.0 or less freshwater shrimp cannot survive, at pH level 5.5,
bottom dwelling bacterial composers cannot survive and begin to die, causing
non-decomposed leaf litter to lie on the bottom and deprive plankton of food
supply (Meric, 2016).
Acidic rain happens when acidic pollutants, sulfur dioxide (SO2),
and nitrogen oxide (NOx) precipitate in the form of rain (Meric, 2016).
The high values of trace metals (Fe, Al, Cu, Zn, Pb, Cd) in
rainwater samples are due to long-range atmospheric transport of anthropogenic
activities, these include industrial activity, coal combustion and automobile
exhaust fumes (Meric, 2016).
These elements are responsible for the catalytic activity of rainwater.
Organic compounds are present in the gas and aerosol phase,
both the processes of gas and particle scavenging are important paths of
atmospheric deposition of these compounds (Meric, 2016).
In rainwater samples the concentration of organic pollutants can vary considerably
due to seasonal transport of the radionuclides, the highest activity
concentrations are in the winter months and are due to the wind direction (Meric, 2016). Natural fires and
volcanic eruptions are the major natural sources of polycyclic aromatic
hydrocarbons. Many processes can be considered as the source: industrial
emissions from catalytic cracking, automobile exhaust emissions and tyre
degradation (Meric, 2016).
Pesticides are a group of organic pollutants which reach the atmosphere through
three main pathways: volatilization during and after application, transport of
soil particles and dust loaded with pesticides, and losses during pesticide
manufacturing processes (Meric, 2016)
Microbial pollution is a major source
of pollution into our water systems, particularly in water reuse plants.
Pathogens are found primarily in the faeces of birds and mammals that have
access to the water reservoir.