Some chemicals are not easily removed from a plant or animal once they have been taken up. They might be difficult to break down, or they may not be eliminated well through processes like urine excretion. Instead, these chemicals bioaccumulate, with levels building up in the plant or animal over time.
Bioaccumulation can happen when a plant or animal absorbs the bioaccumulative chemical from its surroundings (for example, through water) and when it eats another plant or animal that already has built up levels. Because of this, animals at the top of the food chain – like polar bears – are more severely impacted.
Bioaccumulation is a problem because the levels of the chemical that build up in a plant or animal can be very high. Toxic effects that might not be seen at environmental levels emerge when the bioaccumulated level becomes high enough. This means that a chemical could pose a higher risk than it would otherwise seem, so it is important that this is taken into consideration.