BAR HARBOR, Maine — Scientists have known for some time that exposure to even low levels of arsenic can impair the development of immune systems in embryonic stages of life, but according to researchers the biological mechanism of how this might work has been unknown.
That is, until now. In a study of how low levels of arsenic can affect the embryonic development of zebrafish, Mount Desert Island Biological Laboratory scientists Carolyn Mattingly and Antonio Planchart found that 99 of the fish genes had their functions suppressed by the chemical, which can be poisonous in large doses. Of those 99 genes, 19 are associated with immune systems and cancer both in fish and in humans.
The results of Mattingly and Planchart’s study are published in the June 2009 issue of Environmental Health Perspectives, according to a prepared statement released Wednesday by MDI Biological Laboratory.
Jerilyn Bowers, spokeswoman for MDI Biological Laboratory, said Wednesday during a phone interview that the study suggests that exposure of embryos to arsenic might lead to increased susceptibility to many diseases later in life, including cancer.
“This is the first time [scientists] have shown how low doses [of arsenic] affect the expression of these genes,” Bowers said.
According to Bowers, Mattingly and Planchart’s findings reinforce previous studies that indicate even low levels of arsenic exposure in embryos can have long-term consequences for the immune systems of those organisms.
In 2006 the federal Environmental Protection Agency set a maximum level of 10 parts per billion for arsenic in drinking water that is still considered safe to consume, Bowers said. Mattingly and Planchart used lesser concentrations of arsenic in some of their studies but found that the chemical can impair gene expression in em-bryos, even though identical concentrations might not have any visible effects on the health of adults.
Mattingly and Planchart indicated in the release that more research needs to be done before any conclusions can be made about exactly how arsenic exposure affects immune system development.
“The levels that are deemed ‘safe’ may actually be having effects at the molecular level that we don’t understand, and therefore we do not know what the consequences may be,” Planchart said in the release.
Mattingly indicated in the statement that each fish that is exposed to arsenic might not suffer from the same symptoms later in life.
“With these low doses you don’t get deformed fish, but there are potentially damaging effects, which may vary with the individual organism,” Mattingly wrote.
Bowers said that Mattingly and Planchart are not calling for a reduction in the maximum levels of arsenic allowed in drinking water. The data in the study are only preliminary, she said, and they need more funding before they can further explore how arsenic affects gene expression.
According to the MDI Biological Laboratory statement, the zebrafish genome has been fully sequenced, which makes it relatively easy to find genes that are similar to those in humans. Zebrafish make for good subjects in such medical studies because their eggs and embryos are large and transparent and because their fertilized embryos develop into free-swimming fish within three days, the statement indicated.