Polluted usually means to have exceeded a standard of cleanliness. (EG "the drinking water is polluted with MTBE" (MTBE "in drinking water" standard for Pa is 20 ppb, so the water IS polluted with MTBE when the concentration of MTBE reaches 20PPB)
Contamination recognizes that a chemical has been released into the water but is only measurable , its still not reached the standard by which the water becomes polluted.
Other than when we speak of reaching a standard in water, soil,or air, the two terms can often be used interchangeably.
In reality though, the word "polluted" is becoming an outdated term in environmental sciences.