Bioaccumulation is when harmful substances accumulate in an ecosystem. This could be really be dangerous. An example of one of this harmful substances are pesticides. When an organism absorbs one of this harmful substances it could accumulate in it. Once another organism eats the organism that absorbed the harmful substance let's say a pig. WE might eat the pig that got the harmful substance and give it to us. It could seriously make us unhealthy. Using less pesticides would help the environment.