Their results also suggest that it's not any one pollutant that drives this effect -- though traffic-related #pollution, #ParticulateMatter, certain industrial pollutants and certain #HeavyMetals and #petrochemicals stand out -- but rather an accumulation of many small effects.

This makes a lot of sense to me. It also suggests that regulations that focus on one toxic exposure at a time, rather than #CumulativeImpacts, are absolutely insufficient to keep children safe.