Scientific advancements have led to the introduction of many new chemicals into daily life. Unfortunately, along with their benefits, some of those chemicals have brought problems with toxicity. One group of chemicals that has faced this challenge is called polybrominated diphenyl ethers (PBDEs); they have been widely used as fire retardants but are now restricted due to their toxicity and tendency to accumulate in organisms.

Surprisingly, these complicated chemicals are also made naturally. In some cases, the natural compounds actually exhibit higher toxicity than their man-made counterparts. These naturally occurring chemicals are found across all levels of the marine food-chain, from cyanobacteria to whales, and they have also shown up in humans.

Oddly, most of the chemicals come from sponges that live in the tropics. PBDEs can account for more than 10 percent of the sponge’s tissue by dry weight, and these sponges also harbor other related polyhalogenated compounds. Although scientists have been aware of the natural occurrence of PBDEs in these sponges, little has been known about how they were made. In a recent investigation published in Nature Chemical Biology, researchers have found out that the toxic chemicals aren’t the sponges’ fault. Instead, bacteria living inside the sponge produce them.