A common chemical used in thousands of products to help save us from fire, and which has even passed into human body fluids, could be killing fish say scientists.

Baylor University environmental health researchers tested various mixes of the fire retardant chemical found group polybrominated diphenyl ethers (PBDEs) on zebrafish during early development and found developmental malformations, changes in behaviour and death.

Published in the next issue of Environmental Toxicology and Chemistry, this is the first study to test a variety of PBDE mixtures on zebrafish.

PBDEs are used in everything from blankets to furniture and even in food wrappings. Tests have found PBDEs in human breast milk and cord blood and studies have shown children with high levels of PBDEs in their umbilical cord at birth scoring lower on tests between one and six years of age. California started prohibiting the use of PBDEs in 2006.

The PBDE group contains more than 200 possible substances, known as congeners. Congeners are considered low if they average between 1 to 5 bromine atoms per molecule.

The Baylor team tested six of these congeners on embryonic zebrafish and recorded their results, finding effects ranging from changes in behaviour such as a reduction in swimming time, to serious malformations and death. They found that lower brominated congeners were more toxic than higher brominated congeners and two particular types of PBDE were particularly dangerous.

''While most PBDEs have either been banned or phased out throughout the world, it may be more beneficial to identify congeners of concern rather than replacing these compounds with chemicals of unknown biological interactions,'' said Dr. Erica Bruce, assistant professor of environmental science at Baylor who is an expert in environmental chemicals and their effects on public health.

''Alterations in early behaviour may potentially be due to disruption of thyroid hormones. Thyroid hormones play a vital role in the development of the cholinergic system and this study gives insight into biological interaction within a few hours of exposure. The observed hyperactivity may be due to over-stimulation of the cholinergic system,'' Bruce said.