What is the main concern with persistent organic pollutants (POPs)? a.
They are only found in plants, and they disrupt photosynthesis.
b.
They quickly break down into more harmful pollutants.
c.
Although they are rarely found, they are very toxic.
d.
They can be concentrated in an organism’s fat tissues.
e.
They are soluble in water and cause large-scale problems.

d. They can be concentrated in an organism’s fat tissues.

This is referred to as biomagnification -- the POPs become more concentrated as they move from one animal to another. This is a main concern because even trace amounts, in animals at the bottom of the food chain, can cause toxicity to animals at the top of the food chain.

d.) They can be concentrated in an organism's fatty tissue.

Explanation:

Other reasons:

They have a carbon-based molecular structure, containing highly reactive chlorine

Most are manufactured by humans

They are persistent in environment, they do not easily break it down

Polluting and toxic

They occur in forms that allow them to be transported by wind, water, and sediments for long distances.