Showing posts with label Oceans. Show all posts
Showing posts with label Oceans. Show all posts

Thursday, July 24, 2014

Bioaccumulation and Biomagnification

Heavy metals (mercury, lead, cadmium), pesticides and herbicides (such as DDT) and endocrine-disrupting chemicals (PCB’s and BPA’s) do not readily biodegrade. These are fat-soluble substances that are stored in organisms and are not quickly broken down by bacteria or other decomposers. Bioaccumulation is the process by which persistent pollutants accumulate in the fatty tissues of organisms. These pollutants are absorbed at a greater rate than they are released and therefore build up within the individual organism. Biomagnification is the process by which persistent pollutants increase in concentration up a food chain. So secondary and tertiary consumers have higher concentrations than producers and primary consumers.

This phenomena has been observed with DDT, causing the thinning of eggshells in raptors, such as the threatened Peregrine Falcon. Rachel Carson, a marine biologist and conservationist,  made the American public aware of the environmental problems caused by synthetic pesticides, such as DDT, in her famous book, “Silent Spring”. DDT is now prohibited in most developed countries.

Mercury has been shown to bioaccumulate in marine food webs, affecting higher order consumers, such as dolphins, sharks and swordfish. As such, Food Standards of Australia and New Zealand recommend that the intake of certain types of fish is limited.

Content Courtesy : vceenviroscience

Thursday, July 17, 2014

Small Plastics Pose Big Problem

A decade or so ago, scientists first discovered that tiny pieces of plastic debris discarded by human civilization — some only a few thousandths of a millimeter in size — were finding their way into the oceans. But since then, it’s become increasingly apparent that microplastics, as the miniscule trash is called, represent a potentially huge threat to aquatic animals, according to an article in the July 11 edition of the journal Science.

The article, by marine scientists Kara Lavender Law of the Sea Education Association in Woods Hole, Mass. and Richard C. Thompson of the UK’s Plymouth University, notes that researchers increasingly are focusing upon the danger from microplastics, because their size makes it possible for a huge range of organisms — from large marine mammals, fish and birds to zooplankton — to ingest them. (Indeed, a 2012 study found that they pose a health threat to Baleen whales.)

Photos: Life on the Ocean Floor Garbage Patch

A report issued in June by the Global Ocean Commission estimated that 10 million tons of plastic is dumped into the oceans each year. Some of the plastic is discarded into waterways and then is carried into the ocean, but it’s also lost or discarded at sea by ships, the article notes.

Larger plastic items degrade to form microplastic, but some of the particles also are being put directly into the sea, because bits of cosmetic beads and clothing fibers are small enough to pass through wastewater treatment systems.

Once in the oceans, the particles are transported far and wide in a complex pattern that is difficult to predict. However, scientists have found very high concentrations in the subtropical gyres -- that is, areas where currents rotate rapidly — and in basins such as the Mediterranean.

Microplastics are themselves toxic, but they also soak up harmful chemicals that contaminate the ocean, such as DDT and PBDEs, so that they deliver a concentrated dose to the animals who ingest them. Marine scientists also worry that microplastics will end up in seafood-eating humans as well.

Video: How Much Trash is in the Ocean?

Microplastics are just one of the environmental woes afflicting the world’s oceans, and pushing them perilously close to ecological collapse, according to an article published last week in Foreign Policy, a political science journal.

Solving the problem is difficult because 65 percent of the oceans are outside the territorial waters of individual nations, and have become the equivalent of a chaotic, lawless “failed state” such as Somalia on land, the Foreign Policy article argued.

Content Courtesy: Discovery