My real concerns are in the quality of the seed being fed more so than contamination, the quality of the water, even with supplements, also I feel that the timing of feeding supplemented foods should be at random times/days and not at a regular time. The timing issue to me means that if you feed at the same time/day the birds will expect to receive their treats as it may and possibly stress if you deviate from the routine [ you stop for dinner or enter birds at a show or for any good reason]
Weather related issues, such as too warm in the summer or too dry [ using improper heat sources thereby drying the air] may affect hatchability. Weather changes are less likely to affect the birds overall as long as drastic changes are not observed. The birds are far more aware of weather swimgs than any of our high-tech equipment can forecast.