By Matt A. Barr
Think of all your favorite fireworks, fertilizers, detergents, and sewage pits. Got them all in your head? Great. Now think of all your favorite bones, teeth, DNA, RNA, and cell membranes. Finally, think of all your favorite plants and algal blooms. What do these things have in common? Phosphorus, of course. This versatile element is critical to all life, and here at the School of Earth and Atmospheric Sciences, it is taken very seriously by Dr. Ellery Ingall and his team of researchers.
Due to its high reactivity (it explodes upon contact with air), phosphorus does not occur naturally as a free element on Earth. Instead, it’s most prevalent in mineral form as phosphates – one phosphorus atom with four oxygen atoms attached. These phosphates are mined and refined for use in agriculture and industry. One of the most common destinations for refined phosphate is fertilizers. While these fertilizers do serve a purpose in large-scale farming activities, they can ultimately end up in waterways and lead to algal blooms that threaten the health of freshwater and certain saltwater environments. Phosphates can also compose aerosol particles that are transported through the atmosphere and deposited in ecosystems that may be incapable of supporting excess phosphorus.
Phosphates form the backbone structures for DNA and RNA though, and phosphorus, separated from its mineral structures by organic metabolic processes, acts as a limiting nutrient in many terrestrial and marine ecosystems. This latter role makes the availability of phosphates to organisms a significant factor in determining any growth in those ecosystems.
The Eastern Mediterranean Sea is one such ecosystem that Dr. Ingall and his research team consisting of Amelia Longo, Julia Diaz, Michelle Oakes, and Laura King have focused on due to dust plumes that are deposited there from continental Europe and Northern Africa. The winds over Europe and North Africa gather up the dust and other aerosols containing phosphates and transport them to the Eastern Mediterranean. In a region such as this where phosphorus content would otherwise be relatively scant, it’s easier to observe what effects result from increased phosphorus deposition.
Specifically, phosphorus in aerosols – the microscopic particles that compose the dust plumes – is the subject of the Ingall Lab’s research. He and his team use a synchrotron located at Argonne National Laboratory to identify the composition, mineralogy, and solubility of different phosphorus species present in aerosols from the dust plumes. The synchrotron is a particle accelerator that exposes the aerosol particles to high energy X-rays. Using these X-ray measurements, Dr. Ingall can characterize an entire plume with the information derived from a few small samples. Amelia Longo led the effort to understand these plumes. It was determined that phosphorus compounds from the European sources were much more soluble in water and, therefore, impacted growth in the eastern Mediterranean to a greater extent than those from North African sources. This came as something of surprise because previous studies and years of satellite data showed that higher quantities of phosphorus were being deposited by the North African plumes. While it was true that more phosphorus was coming from the North African plumes, this phosphorus was much less soluble than what was present in the European plumes, meaning relatively little of the North African phosphorus was affecting the growth of aquatic organisms in the region. Furthermore, the more soluble European aerosol phosphorus was organic in nature and appeared to originate from bacterial sources, whereas the less soluble North African phosphorus was locked up in minerals and lacked organic components.
Using the synchrotron, Dr. Ingall and his team have analyzed a variety of sample mediums for elements other than phosphorus as well. Before applying this technique to the study of phosphorus, Dr. Ingall was involved in researching iron, another limiting nutrient in the oceans. Taking samples from sites across the world and studying them with the help of the synchrotron, Dr. Ingall has identified how iron is used by diatoms whose activities greatly affect the availability of iron for other marine organisms. In Antarctica, these diatoms – microscopic unicellular organisms – appear to be storing iron in the silicate shells they develop as a barrier between themselves and the water. The exact purpose for this is unknown because, according to what Dr. Ingall and his team have observed, the iron stored in their shells is more than what the diatoms require for typical metabolic activities. Research into this question is still ongoing and has been primarily the work of Amelia Longo, who just completed her Ph.D. and Julia Diaz, one of Dr. Ingall’s former grad students, who is now an assistant professor at the Skidaway Institute of Oceanography in Savannah, Georgia.
Along with his studies of phosphorus and other elements in aerosols, Dr. Ingall is in the process of developing new research into the composition of urban aerosols. In conjunction with Dr. Rodney Weber, an atmospheric chemist here at EAS, Dr. Ingall hopes to use the power of the synchrotron to analyze aerosol samples taken from right here in Atlanta. Characterizing the components of these aerosols can go a long way towards understanding the health risks associated with increased human exposure to toxic metals present in aerosol pollution. It may also shed light on some of the lesser-known atmospheric processes that cause the reduction of those metals. This reduction – an exchange of electrons between two species – typically results in these metals having higher solubility, making them more susceptible to dissolving in waters that ultimately end up in our water supply.