August 2009, Vol. 21, No.8
Lessons in Metal Management
Many people are aware of the risk involved with consuming too much mercury. But the intricacies of how these particles move through the environment and accumulate to create this potential risk — particularly when it comes to the minuscule nano variety — has even the top scientists puzzled. Just how does this metal eventually end up in high levels in the fish on your dinner table? And what, if anything, can we do to prevent it? Answers to these questions are coming from an unlikely source.
Eileen Jang, a 17-year old student from North Carolina, is making breakthroughs in the relatively new field of nanogeoscience. By examining the transport and bioaccumulation of mercury sulfide, the precursor to methyl mercury, on a nanoscale, her research is deepening the understanding of this potentially harmful element in its aqueous state.
While other students her age might have spent the year enjoying their last days of high school, Jang spent her free time in a lab at Duke University (Chapel Hill). It is here that Jang was able to create tiny particles of mercury sulfide about a billionth of a meter wide, and using this material as her base, perform a battery of tests to determine how aggregation was impacted by salinity and organic matter naturally found in waterbodies.
Jang’s findings led her to believe that in natural environments, salinity might play a role in controlling mercury sulfide nanoparticles. Results indicated that, to a point, higher salinity equates to higher particle collisions, in turn allowing for greater aggregation. What’s more, she also discovered that the presence of natural organic acids, specifically those in the sulfhydryl group, have the inverse effect. They were able to stunt aggregation by reducing the amount of successful particle collisions that induces attachment.
Jang’s groundbreaking research won her the top prize at the 2009 U.S. Stockholm Junior Water Prize Competition, an event that draws the brightest young researchers from across the United States who are exploring water issues. With this honor also comes a seat at the prestigious international competition, held annually in Stockholm, Sweden. Jang will go on in August to represent the United States at this event, share her research with the global water community, and network with students from around the world who also are tackling some of today’s toughest water problems.
“This field of research is important because we may understand how metals behave on the micro or macroscale, but we have little understanding of how metals behave on the nanoscale,” Jang said. “The chemistry and toxicity may be different at this size, and currently, nanoparticles can even pass through conventional treatment filters and be misclassified as soluble. We need to dig deeper into this newly emerging field so that future research can use this knowledge to find ways of accurately modeling metal contamination in water and preventing dangerous metals on the nanoscale, like mercury, from getting into our drinking water and poisoning our bodies.”
Next, Jang hopes to study how methylation rates are influenced by mercury sulfide nanoparticle processes and how mercury sulfide nanoparticles affect bioavailability of mercury in the environment, both of which will be important factors in the prevention of methylmercury poisoning in humans and other organisms. This time, she’ll likely be spending her spare time at a lab at Yale University (New Haven, Conn.), where she plans to attend school this fall.
Keeping the Quagga Mussel at Bay
Idaho is spending $5 million to keep its mussels from growing. Fears of the invasive quagga mussel have prompted the Idaho Legislature to grant the sum to combat the species from entering the state’s watersheds, according to a news release from the U.S. National Academies.
Carried to the United States in transoceanic ship ballast from its native Ukraine, quagga mussels reach only 40 mm (1.6 in.) in size but pack a powerful punch when it comes to affecting native ecosystems, according to a U.S. Geological Survey (USGS) species factsheet.
Much like its relative, the zebra mussel, the quagga has already spread itself throughout the Great Lakes region of the northern United States. Feeding on phytoplankton, the quagga takes food sources from zooplankton and alters the natural food web. Other ecosystem-changing effects result from the quagga’s water filtration and production of pseudofeces, the factsheet says.
Also like the zebra mussel, the quagga presents an alarming threat to water infrastructure. Due to their tendency to colonize hard surfaces, quagga can quickly clog intake pipes and screens, reducing pumping ability. But unlike the zebra mussel, which lives up to a depth of 15 m (50 ft), the quagga can survive at twice that depth. Facilities that buried pipes out of the reach of the zebra mussel did not plan for and could be adversely affected by growing quagga populations, according to the factsheet.
According to Amy Benson, a USGS fishery biologist who co-authored a report on the quagga mussel, controlling quagga populations would be “extremely beneficial for water treatment facilities using surface waters.”
“The mussels are notorious for forming colonies inside pipes and severely constricting water flow, even to the point where the pipe may be totally occluded,” Benson said. She also noted that the mussel’s byssal threads, which are used to attach the mussel to hard surfaces, can damage the integrity of pipes and screens over time, leading to costly repairs for the facilities and communities that use them.
Though quagga mussels are mostly concentrated in lakes Erie, Michigan, and Ontario, according to Benson, it is only a matter of time before they spread throughout the rest of the country. They already have been found in Lake Mead in Nevada, which supplies much of the U.S. Southwest with water, leading to quagga sightings in reservoirs in Southern California and Arizona.
The best way to control the spread of quagga mussels is public education, Benson says. “The bottom line is drain, wash, and dry all equipment after use in any waters, especially if from known infested waters. A combination of pressure washing, onsite inspections, and permits will go a long way in preventing the spread of quagga mussels.” There is also some promise in controlling quagga populations with a commonly found bacterium that is safe to humans. According to a study for the Idaho Invasive Species Council (Boise), combating the quagga after it has been introduced into an ecosystem could cost as much as $94 million.
Texas Researchers Look Above and Below Ground for Water Savings
Worries of drought conditions and increasing water consumption in the U.S. Southwest have spurred researchers at the Texas AgriLife Research and Extension Center (Uvalde) to study groundwater recharge, according to a news release from Texas A&M University (College Station).
Through the center’s Precision Irrigators Network, founded in 2004, researchers have partnered with a network of local agricultural producers to find solutions to possible water restrictions while still maintaining high crop quality and quantity.
Together, they collect field data on soil type, soil moisture evaporation, rainfall and climatic factors, and growth stages of crops. They then use the data to develop new, more efficient methods of irrigation, the news release says.
Through their combined efforts, they hope to produce significant water conservation. “The network was formed with the goal of saving millions of gallons of water annually by reducing irrigation water use by as much as 20% in the future,” said Bill Holloway of Texas AgriLife Research.
Researchers believe their work will translate into water savings not only in south-central Texas but around the country and internationally in regions with similar climate, soils, and water sources, said Diane Rowland of Texas AgriLife Research.
Other scientists at the center are focusing on water issues that lie below ground. Jason West, an ecosystem ecologist, is researching stable isotopes of well water to improve methods for aquifer recharge. He is also looking at ways of distinguishing different types of aquifers using two unique local aquifers — the Edwards and the Carrizo–Wilcox, the news release says.
“Stable isotopes record the evaporation and condensation histories of water and naturally ‘label’ different waterbodies,” according to West. His research would provide needed insight into the functioning and makeup of these underground waterbodies.
With a fuller knowledge of these subjects, water districts will be able to address problems of water shortages effectively in the future and, according to Holloway, ensure “an adequate supply of this precious natural resource in years to come.”
©2009 Water Environment Federations. All rights reserved.