Sentence:  Work historically performed by toxicologists has provided an impressive list of endogenous and <WSD>exobiotic</WSD> compounds termed peroxisome proliferators (PP) which were so named for their ability following chronic high dose administration to rodents, to increase the number and activities of an essential intracellular organelle termed the peroxisome. 
Meaning of the word marked with <WSD> tags:  From outside of an organism or from the substrate.