ESE Discovers Oil Arsenic Hazard

In a paper published in the journal Water Research a team of scientists from the Department of Earth Science and Engineering announce the discovery of a new hazard from marine oil spills.

In a paper published in the journal Water Research a team of scientists from the Department of Earth Science and Engineering announce the discovery of a new hazard from marine oil spills. The research, conducted by Wimolporn Wainipee, Dominik Weiss, Mark Sephton and Richard Court, reveals that oil spills increase arsenic levels within sea water leading to an additional, long-term environmental hazard.

Arsenic is a chemical element that is toxic in high concentrations and even exposure to low concentrations is harmful if over long periods. Arsenic occurs naturally in seawater but its concentration is kept in check by minerals in ocean sediments. Certain minerals act like sponges for heavy elements due to their unique surface properties - the mineral goethite, an iron oxide mineral containing water molecules is particularly important in adsorbing arsenic. This natural filtration system ensures that arsenic levels within our planet's oceans do not become toxic for marine life.

The new research examined the adsorption of arsenic on goethite and showed that under low water pH goethite can adsorb more of the toxic element. However, the study also showed that presence of oil significantly reduces the uptake of arsenic by goethite and makes this mineral less able to lock it away from seawater.

Marine oil spills have a double impact on seawater arsenic. Oil contains additional arsenic that increases its concentration in seawater, and it reduces how much arsenic can be removed by ocean sediments. Wimolporn Wainpee, a PhD researcher in ESE says:

"We carried out our study before the leak in the Gulf of Mexico occurred, but it gives us a big insight into a potential new environmental danger in the region. Thousands of gallons of oil are leaked into the world's oceans every year from big spills, offshore drilling and routine maintenance of rigs, which means many places may be at risk from rising arsenic levels, which could in the long run affect aquatic life, plants and the people who rely on the oceans for their livelihoods."

The affect of arsenic on the marine ecosystem is compounded by its long-term accumulation. Organisms such as molluscs concentrate arsenic to high levels which, when eaten by other animals, enters the food chain, affecting fish, marine mammals and even sea birds. In marine organisms arsenic poisoning can disrupt photosynthesis in marine plants and result in birth defects and behaviour changes in aquatic life. Over long periods even humans who eat sea foods contaminated by arsenic can be at risk.

Prof. Mark Sephton from ESE highlights these long term hazards: "We can't accurately measure how much arsenic is in the Gulf at the moment because the spill is ongoing. However, the real danger lies in arsenic's ability to accumulate, which means that each subsequent spill raises the levels of this pollutant in seawater. Our study is a timely reminder that oil spills could create a toxic ticking time bomb, which could threaten the fabric of the marine ecosystem in the future."

Dr Dominik Weiss from ESE also notes "Individually, arsenic and oil are damaging to the environment, but together the effects are magnified. Our research is a good example of Earth Systems in action. As we strive to increase our knowledge of how the environment works, multidisciplinary science is becoming increasingly important. Chemistry, geology and biology all interplay in the oceanic environment.

In the future, the researchers plan to analyse other minerals such as clays and carbonates that are sediments on the ocean floor. Sediment content varies from ocean to ocean and the researchers will analyse how oil affects their ability to bind to arsenic after a spill.

Related Links

• Journal of Water Research

Personnel

• Richard Court
• Mark Sephton
• Dominik Weiss
• Wilmolporn Wainipee