CHEMICAL FATE AND TRANSPORT IN THE ENVIRONMENT

Chemical fate and transport in the environment

Chemical fate and transport in the environment

The term speciation has often been used to indicate the analytical activity of identifying chemical species and measuring their distribution. Sometimes, it is used to indicate that a method gives more information on the form in which the element is present than other more commonly applied techniques (e.g., measuring distinct organ mercury compounds as opposed to a total mercury determination). In order to avoid confusion, we recommend using the term speciation analysis when referring to the analytical activity of identifying and measuring species. the term speciation is also used to indicate the distribution of species in a particular sample or matrix (Cavanaugh, 2002).

Importance of speciation in chemical pathway in environment

The term speciation, originally coined to describe evolutionary processes leading to new biological species, is now also used in the chemical sciences to refer to the distribution of the different forms or species of a particular element. Speciation is also often used to describe the measurement of chemical species, although use of the more descriptive speciation analysis has been advocated.In environmental chemistry, a knowledge of speciation is critical to understanding the transport, accumulation, bioavailability and toxicity of elements within and between the environmental compartments of air, soil, water, sediments and biota. speciation encompasses all chemical elements, although for historical reasons the term is more commonly used for studies dealing with metals or metalloids(Cavanaugh, 2002). The term became more widely used in the environmental sciences from the 1960s, when studies on mercury-contaminated aquatic systems showed that inorganic mercury was readily methylated by natural microbial processes to methylmercury, a species of mercury more bioavailable to organisms and more toxic to humans than was inorganic mercury. Similar studies followed for other metals and metalloids. These studies demonstrated that knowledge of speciation was integral to understanding the behaviour, fate and effects of metals in environmental systems. Increasingly, the term speciation is being applied to non-metals as well, for example investigation of halogen or nitrogen speciesin atmospheric processes. (Hemond, 1999)

Speciation studies initially focussed on measuring the concentrations of particular operationally-defined classes of chemicals, and in some cases specific molecular forms. Later studies investigated their formation, reactivity and bioavailability. Such studies are becoming increasingly multidisciplinary linking environmental chemistry both to the life sciences such as ecology, ecotoxicology and microbiology, and to other physicalsciences through research on diffusive or hydrodynamic transport of species, and crystallisation and sedimentation processes (Childess ,2000).

This multidisciplinary approach is necessary to fully understand the behaviour of chemicals in our global environment, and to evaluate their impact on both ecosystem and human health. The speciation data necessary to gain such a profound understanding of the chemistry of the environment are obtained from a variety of techniques including both equilibrium and dynamic. peciation may also be useful in studying element toxicokinetics, since it is well known that hexavalent Cr is taken up more than the trivalent form, and that species of the same metal are differently partitioned in ...