Why do predator fish contain the highest methylmercury concentrations?
Methylmercury is taken up by stream biota primarily through the food they eat. Methylmercury is not readily excreted, so when an organism consumes another organism, it retains and accumulates the mercury in that organism. Predator fish are eating at or near the top of the local food chain, so they acquire all the methylmercury that has been accumulated at lower levels of the food chain. Additionally, predator fish are longer-lived than organisms lower in the food web, so they have more time to accumulate more mercury over their lifespan.
