This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Heavy elements such as arsenic and selenium enter the environment through natural and manmade processes and then become available to living things. Selenium, and possibly also arsenic, is an essential trace element for mammals, but both are also well known for their toxicity. The molecular form of any element critically affects its transport, bioavailability and toxicology, in other words how it interacts with the environment and ultimately with man. Knowledge of molecular form is also required in order to propose effective remediation strategies. X-ray absorption spectroscopy (XAS) can investigate the chemical form of an element essentially without pretreatment of the sample, and hence can yield in situ information about chemical form. XAS imaging is a powerful microprobe technique in which the sample is raster scanned in a small beam at energies sensitive to the different chemical forms in order to generate maps of those species. XAS and XAS imaging will be used to investigate the molecular form and spatial location of predominantly arsenic and selenium in organisms with environmental relevance. In one set of experiments, the molecular mechanisms of hyperaccumulating plants will be studied;these plants take up and store high levels of arsenic or selenium in their tissues and offer potential for phytoremediation. Simple insect ecosystems will also be studied, to examine how selenium is bioaccumulated and biotransformed, either alone or in combination with mercury. Finally, zebrafish larvae exposed to non-lethal levels or arsenic and mercury will be studied to determine the localization and speciation of the heavy elements. The proposed program should provide valuable information on how heavy elements, and arsenic and selenium in particular, are chemically transformed within the environment.