EVEN deep-sea creatures aren鈥檛 safe from the notorious pesticide DDT. Large amounts of DDT-laden soil are moving through an underwater canyon and out into the open sea off California.
Although DDT was banned by the US and other industrialised nations in the 1970s, it is long-lived and is still found in soils and sediments as well as human and animal tissues around the world. But Charlie Paull and his team at the Monterey Bay Aquarium Research Institute in Moss Landing found that it had penetrated further than anyone realised. They found high levels of DDT in sediment 3200 metres below the ocean surface on the floor of Monterey Canyon, which extends over 80 kilometres off the coast of Monterey.
DDT was first used in nearby farmlands as an agricultural pesticide in 1945, so the soil at the bottom of the canyon must have been running off farmers鈥� fields and into rivers and streams for the past 57 years, say the researchers. They took core samples throughout the canyon, and saw a clear pattern of contaminated sediment starting at the canyon鈥檚 head and moving through it.
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鈥淲e think of things going on in agricultural lands as irrelevant [to the deep sea], but this data suggests that the timescale is fast enough for these effects to be played out over a human lifetime,鈥� says Paull.
The scientists aren鈥檛 exactly sure how long the soil takes to move through the canyon, but suggest it could come from a turbidity flow, a kind of underwater landslide that lasts only minutes.
The scientists have submitted their results to Geo-Marine Letters, and are planning tests to determine how far the DDT-laden sediment is moving along the ocean floor. But figuring out how much of it is getting into the tissues of deep-sea animals is a much harder project. 鈥淚t鈥檚 going to be dicey,鈥� says Paull.