Washington, July 15 : Scientists have determined that tons of dust from Africa's arid Sahara and Sahel regions could be polluting oceans in the Caribbean and southeastern US.
According to a report in National Geographic News, the dusty clouds carry contaminants like metals, pesticides and microorganisms-potentially disastrous news for coral reefs and other marine animals already stressed by warming waters.
Desertification and changing land-use patterns can put more dust into the air. Industrialization, pesticide use, waste burning, and other practices have produced air pollutants that ride with that dust to far-flung locales.
"We're trying to actually look at what is in these African dust air masses when the get over to the Caribbean," said Virginia Garrison, an ecologist with the US Geological Survey in St. Petersburg, Florida, who studies how the dust travels.
"We're at the baby-step stages of trying to see how this dust and this stew of things may be affecting organisms-including humans-in downwind areas," she added.
Air-quality data from a network of sampling sites have revealed intriguing results.
For instance, Caribbean air samples during African dust events may hold two to three times as many microorganisms, such as bacteria and fungi, as samples taken from the same spot during other periods.
In Florida, the Africa-influenced air conditions sometimes deteriorate below US air-quality standards.
Air-quality testing in Mali, the US Virgin Islands, and Trinidad and Tobago has also revealed traces of pesticides, including DDE-a breakdown product of DDT, which is still used as an insecticide in some African countries.
Pesticides are of particular concern to coral reefs because they can interfere with the tiny animals' reproduction, fertilization, or immune function.
These contaminants were highest in Mali and lower in the downwind areas of the Americas. Six pesticides were found at each one of the test sites, according to Garrison. "And there's been very, very little work that has been done on the concentrations of any of these pesticides or PCBs (and how) that would impair coral or coral reef organisms," she added.
According to Andrew Negri, of the Australian Institute of Marine Science in Townsville, "The pesticides associated with African dust are primarily insecticides. These can affect the coral host directly."
"We have found that two of the identified insecticides, chlorpyrifos and endosulfan, can reduce the settlement and attachment of coral larvae to the ocean floor at very low concentrations," he said.
"I would be particularly concerned if storms containing insecticide-contaminated dust were to occur upwind of coral reefs around spawning time," he added.