Biological magnification is when the concentration of something (like a chemical or something hazardous) is more concentrated within the levels of the food chain. For example, you have a fly that was consumed by a frog. The fly had a toxin within their body and now the frog has it. It continues to become more concentrated in the frog. The frog is consumed by a bird. The birth now has a more concentrated level of toxin. The bird is then consumed by a human. There is now more concentration within the human.
Bio concentration is related to the water. It's when the concentration within the water is filled with a toxin and the life within the water has a higher concentration within their body.