In the first example, because "contaminants" is plural, it is unlikely that all of these contaminants will have the same singular effect. Chances are good that multiple contaminates cause multiple effects.<br /><br />In the second example, the fact that&nbsp;coatings, aggregation, and dissolution on MNPs are three different steps/stages suggests at least three different effects.<br /><br />In my thinking, a singular factor causes a singular result (though it's still possible that a singular factor/event causes multiple results). An atomic bomb certainly has an effect (i.e., wipes out a city: Hiroshima and Nagasaki), but the bomb's effects are multiple: illness among survivors, environmental damage, the mindshift of an aggressive nation into a peaceful one, etc.<br /><br />A stone tossed in a lake creates more than one ripple.