Lead pollution
Much of my research is focused on lead pollution. No safe level of lead exposure has been identified. Even low levels of lead in blood have been shown to negatively affect a child’s IQ, ability to pay attention, and performance in school. Lead is a top risk factor for premature death in the USA, particularly from cardiovascular disease. My work includes spatial studies of modern and persistent legacy lead sources in urban centers and temporal studies examining historical trends of lead pollution.
Spatial Studies
I evaluate distributions of environmental lead and identify lead sources in cities and remote areas. This information can be used to reduce environmental levels and human exposures.
Research highlight:
In a new paper, found here, we report environmental lead levels up to 590 times greater in Portland than rural areas using moss. In addition, older Portland neighborhoods have lead levels about two times those of newer neighborhoods and 19 times higher than rural areas. The study finds that lead from the historical use of leaded gasoline remains a key source of lead in the city, decades after phasing out its use. The highest levels of the city are found near old overhead lead-sheathed telephone cables. We think this lead is being leached from the cables by rain on to the soil and vegetation below. More research is needed to determine if people are being exposed to this lead and how high lead levels are in the soil.
Learn more about how to identify lead-sheathed telecommunication cables and limit your exposure here.
Temporal Studies
I construct global records of lead emissions that span the history of human input using ice and lake sediment records. This work identifies human activities (e.g., rise and fall of civilizations, war, plagues, industrialization) that have perturbed the natural distribution of lead locally, regionally, and globally.
Research highlight:
Temporal studies include the reconstruction of a high-resolution 250-year record of lead isotopes in Greenland ice. This study, available here, found more than 95% of lead in the ice originated from pollution. U.S. lead pollution peaked in 1968, coincident with the highest levels of lead consumption for leaded gasoline.
Find a full list of my publications on my Google Scholar page here.
Examples of past projects:
Tracing of smelting emissions using cadmium, zinc, and lead isotopes
This research uses a combination of cadmium, zinc, and lead isotopes to trace the impact of smelting emissions. We have demonstrated that cadmium and zinc isotopes are fractionated during metallurgical processes and that they have the potential to trace their distributions in the environment. In contrast, lead isotopes are used to identify the ores, with unique radiogenic signatures, processed by the smelter.
An example of this work can be found here.
Development of uranium isotope fractionation as an indicator of uranium immobilization by U(VI) reduction to U(IV)
This research investigates the use of uranium isotopic composition as a tool for evaluating U(VI) reduction to U(IV) by measuring the 238U/235U of groundwaters from a uranium contaminated aquifer at a former uranium mill site in Rifle, CO. We have demonstrated that significant uranium isotopic fractionation accompanies U(VI) reduction during bioremediation and thus, that uranium isotopes provide a powerful tool for quantifying the extent of U(VI) reduction to U(IV) and thus, immobilization.
An example of this work can be found here.
Tracing cadmium, zinc and lead sources in oysters and mussels from Canada, the USA and France
In contrast to efforts focused on the use of metal concentrations, which are limited in their ability to assess metal sources, I used cadmium, zinc and lead isotope ratios to trace the source of these metals in bivalve tissues. I used this technique to determine that despite relatively high cadmium levels in British Columbian bivalves, Cd in their tissues is primarily natural, likely originating from the upwelling of nutrient-rich (and cadmium-rich) waters along that coast. In contrast, I identified cadmium in bivalves from France and the USA East Coast as primarily anthropogenic.
An example of this work can be found here.
