A worldwide pollutant may cause gene loss.

Feb 23, 2009

Nowak, C, C Vogt, M Pfenninger, B Streit, J Oehlmann, K Schwenk and M Oetken. Rapid genetic erosion in pollutant-exposed experimental Chironomid populations. Environmental Pollution doi:10.1016/j.envpol.2008.11.005.

Synopsis by Niladri Basu

A new study suggests that long term exposure to a common water pollutant reduced the genetic diversity of the midge - a common water insect.

Aquatic insects are the foundation of healthy waterways. Other insects, invertebrates and fish depend on the tiny creatures for food. A loss of their genetics is a loss for ecosystem diversity.

The pollutant, called tributyltin (TBT), is a widely used pesticide. While TBT affected the growth, survival and reproduction of the midge insect, the greatest effects were found in the genes. TBT-exposed insects lost gene diversity two times greater than non-exposed insects.

The study provides direct evidence from the lab that pollution may cause genetic loss in nature. The results have "important implications for conservation strategies and ecological management in polluted environments," the authors say.

The study is also important because it mirrors real-world exposure.

Most toxicity studies look at high dose, single generation effects. But, in reality, organisms -- including humans -- are exposed to low-levels of chemicals over long periods, sometimes for many generations. Little is known about how these types of exposures may affect health.

In this study, scientists exposed the midge to TBT at levels found in the environment for 12 generations. They monitored growth, weight, mortality and genetic diversity, which was determined by studying DNA sequences known as microsatellites.

Genetic diversity is the number of different kinds of genetic characteristics in a species. Genes govern an individual's characteristics -- whether external appearances or internal functions. Diversity ensures that a population has a large number of gene variations spread among individuals.

Genetic loss has been reported in nature, in studies on fish, crustaceans (crabs, lobsters) and gastropods (snails). These studies focused on genetic loss caused by changes in habitat and lifestyle. Pollution has seldom been explored as a reason for genetic loss.

Tributyltin (TBT) is a biocide and a known endocrine disruptor. Biocides control and kill organisms.

Before its recent worldwide ban, TBT was used extensively in marine paints to keep barnacles and other marine creatures from growing on ship hulls. In the environment, TBT does not break down and it builds up in food chains. Because of its longevity and widespread use, it is no surprise that TBT pollutes harbors, waterways and animals all over the world.