The hypothesis that the amount of contaminants found in snow decreases in locations situated further away from the city, is proven to be correct.
Children love to play with snow and even eat snow. However, snow in urban areas contain a lot of pollutants. Snow that is yellow, black, brown or pink in color must be avoided completely. There's a reason why the snow appears yellow in color - it's altogether possible that it contains animal urine. If the snow is black and brown, it probably contains large amounts of dirt. Pink snowis probably pink becauseof bacterial contamination.
Try to repeat the experiment in different locations or at different times of the year.
The experiment can also be repeated using rain water instead of snow. Would there be a difference if the snow is collected right at the start of a snowfall?
The clean snow experiment - http://www.examiner.com/x-28900-Mankato-Homeschooling-Examiner~y2009m12d14-The-clean-snow-experiment
Don’t eat yellow snow, or black, or brown, or pink - http://www.treehugger.com/files/2007/11/ask_treehugger_25.php
Basic safety requirements