12. Sand Spit, Baia de Sepetiba, Brazil
This 50-kilometer-long (31 miles) sand spit links the Brazilian mainland near Rio de Janeiro with a small island and encloses a large lagoon, the Baia de Sepetiba. The spit was formed by the lateral movement of sediment along the beach, carried southward by the Brazil current (from left to right). The process of longshore drift is a slow and continuous one, but some coastal geomorphologists think that spits form as the result of single exceptional events (such as a hurricane), rather than through slow and steady accretion.
The shallow water of the lagoon behind the spit is floored with fine-grained muddy sediments, rich in organic material, and a fertile breeding place for shellfish such as oysters. Discharge of industrial effluent from factories along the Brazilian coast of the Baia de Sepetiba has, however, led to the build-up of large concentrations of heavy metals in the sediments. Shellfish further concentrate the metals, and may become unfit for human consumption.
STS-41D, August-September 1984. Picture #14-44-083.