Carl Lamborg used sediment traps to try to find the source of toxic monomethyl mercury (MMHg) in low-oxygen zones of the ocean.The tube-shape traps were suspended at depths above, in, and below the low-oxygen zone and left in place for four days. Particles drifting down through the water fell into the traps. After recovering the traps, Lamborg analyzed the material in them for the presence of elemental mercury and monomethyl mercury. He found very little of either, leaving the source of MMHg in the low-oxygen zone a mystery.