synergism(An ecological association in which the physiological processes of behaviour of an individual are enhanced by the nearby presence of another organism)
synergistic effect of toxic substances(1. A state in which the combined effect of two or more substances is greater than the sum of the separate effects. 2. An effect whereby two toxic substance together have more of an impact than anticipated)
continuous load(The amount or quantity of polluting material found in a transporting agent that flows at a steady rate, in contrast to a sudden or dramatic influx)