Guánica Bay in southwestern Puerto Rico suffered severe industrial contamination throughout the mid-twentieth century due to manufacturing discharge containing high levels of polychlorinated biphenyls, or PCBs. These synthetic organic chemicals are notorious for their environmental persistence and resistance to degradation. When PCBs seeped into surrounding coastal and wetland ecosystems, they accumulated in sediment and aquatic food webs.
The critically endangered Puerto Rican crested toad, which relies on temporary rain-filled breeding pools in the region, faced severe bioaccumulation hazards. Microscopic organisms and insects ingested PCB-laden sediments, transferring concentrated toxins up the food chain to the toads. Exposure to high PCB levels causes endocrine disruption, impaired immune response, and developmental abnormalities in amphibians, threatening conservation efforts to restore the island's only endemic toad species.