Hg Research - A. Carpi

Moore, C., Carpi, A. (2005) “Mechanisms of the emission of mercury from soil: The Role of UV radiation,” J. Geophys. Res., 110(24):D24302.

Abstract: Light has been previously shown to play a role in the emission of mercury from soil; however, the mechanisms involved in this process are not well understood. In an effort to identify the wavelength of light that dominates this process, we conducted extensive laboratory studies of soil mercury flux using a dynamic flux chamber. Mercury fluxes were measured at constant temperature in the dark, under full spectrum radiation (λ = 320-700 nm), and under various radiation bands including 410-700 nm radiation, 320-580 nm radiation, and 320-380 nm radiation. Soil mercury emissions under full spectrum radiation were significantly elevated over dark fluxes in all trials. When UV light was removed from incident radiation (the λ = 410-700 nm condition), fluxes were not significantly different from dark fluxes in two of three trials. Soil fluxes under 320-580 nm radiation and 320-380 nm radiation were significantly elevated over dark fluxes in all trials and were related to radiation intensity in the UV region.

Figure. Summary of all radiation wavelength band trials and zero radiation fluxes plotted with PAR radiation intensity measurements and UV radiation intensity. To compensate for slight natural day-to-day variations in soil flux, fluxes in this figure are reported as a percent of full spectrum flux measured on each day. A 95% confidence band of the full spectrum flux is given in gray at the top of the table. Under full spectrum radiation, PAR intensity was 105 W/m² and UV intensity was 6.2 W/m².

Haidermota, U.S., Nguyen, P.V, Smalligan, M.J, Carpi, A. (2004) “The Effect of trees (Poplar nigra) on soil mercury fluxes,” Materials and Geoenvironment 51(2):897-900.

Abstract: Soils have long been recognized as a significant source of mercury reemission; however, it is only recently that the role of trees on soil mercury fluxes has been examined in detail. We used a modified dynamic flux chamber to examine the effects of trees (Populus x canadensis Moench 'NE-367') on soil mercury emissions. Separate chambers were constructed around the tree soil system and the foliage area to allow mercury emissions to be quantified independently in these compartments. A third chamber was constructed around a separate, identical soil system that was not planted with P. canadensis to serve as a control. Soil and foliar mercury fluxes were examined before and after the addition of dissolved mercury salts to the soil. At the conclusion of the study, poplars were harvested and sampled for mercury transport. Mercury emissions in the tree canopy chamber were not dependent on soil mercury addition and appeared to cycle between emission and deposition in day and night, respectively. Tissue sampling confirmed this finding by showing that soil mercury accumulated in the roots but was not transported through the tree system. Trees did, however, increase the emission of mercury from the soil system and this effect was independent of solar radiation levels.

Figure:Daily Mean Hg Flux for Tree Canopy. No significant change in mercury flux from the foliar canopy was seen after mercury-spiked irrigations began on day 16 (vertical grey lines).

Carpi, A., Chen, Y. (2002) “Gaseous Elemental Mercury Fluxes in New York City,” Water, Air & Soil Pollution 140(1-4):371-379.

Abstract: As with many urban environments, a number of sources of airborne elemental mercury (Hg°) exist in New York City, yet little research has been conducted to examine the flux and sources of mercury in New York. In this study, we conducted ambient monitoring of Hg° at six locations in New York City. Airborne Hg° averaged 3.84 ± 0.10 ng/m³ and 3.70 ± 0.08 ng/m³ in the boroughs of Manhattan and Brooklyn respectively, yet only 2.69 ± 0.03 ng/m³ in a more residential neighborhood in Queens. Both precipitation and ambient temperature were significantly correlated with ambient Hg° levels in New York City, suggesting that the surface emission of mercury from urban surfaces plays a role in urban Hg° concentrations. Local sources were also seen to contribute to urban Hg° levels by leading to ‘spikes’ of Hg° in which elevated concentrations were recorded for short periods of time.

Figure: Boxplots showing the range and distribution of [Hg°] at four sites in Manhattan (M), one in Brooklyn (B), and one in Queens (Q), in New York City.

Carpi, A., Chen, Y. (2001) “Gaseous Elemental Mercury as an Indoor Air Pollutant,” Environmental Science & Technology 35(21):4170-4173.

Abstract: Mercury is not commonly considered a household air pollutant, however a number of potential sources of the metal exist in residential settings. Eleven of 12 indoor sites sampled in this study showed levels of airborne mercury that were significantly elevated over outdoor concentrations (range 6.5-523 ng m^-3). In addition, this and other published research suggest that up to 10% of households may have levels of airborne mercury above the U.S. EPA reference concentration (300 ng m-3) due to historic accidents with mercury containing devices. Exposure to mercury via indoor air is seen as second only to fish consumption as a source of mercury in the general population. Large seasonal changes in indoor mercury levels were identified in this study suggesting that short-term monitoring of mercury-contaminated sites is not sufficient to adequately assess the potential health risks and effectiveness of remediation strategies.

Figure: Indoor Airborne Hg° Concentrations at 12 Sites in the New York metropolitan area.

Carpi, A., Mital, J. (2000) “The Expanding Use of Forensics in Environmental Science,” Feature Article - Environmental Science and Technology 34(11):262A-266A.

Introduction:
On the morning of July 14, 1995, twin infants, barely a few weeks old, werefound shot to death and disemboweled near the town dump in Winnipeg,Manitoba. In the days following the incident, a trail of forensic evidence provedcrucial for identifying and convicting the perpetrators of the crime.

Taken together, the evidence was damning. Eyewitness testimony placed twomen at the dump site on the evening of July 13. DNA tests revealed that blood ona knife in the suspects' possession matched that of the infants. Investigatorsturned to Gail Anderson, a forensic entomologist at Simon Fraser University inBurnaby, British Columbia, to corroborate the eyewitness sighting with the timeof death of the victims. By tracking the life cycle of insect eggs laid in thewounds of the victims, Dr. Anderson established the time of death as the eveningof July 13. The case proceeded to trial, and the judge cited the forensic DNA andentomological evidence as crucial in ordering jail time for the two offenders.

The case highlights a textbook forensic investigation that is unique from thestandpoint of the victims involved—two black bear cubs. Killed for the price oftheir gall bladders on the black market, the young bears yielded a pair of organstoo tiny to have any significant value.

Carpi, A., Lindberg, S.E. (1998) "Application of a Teflon™ Dynamic Flux Chamber for Quantifying Soil Mercury Flux: Tests and Results Over Background Soil," Atmospheric Environment 32(5):873-882.

Abstract. High precision and low blank contamination were achieved with a Teflon™ dynamic chamber for measuring soil mercury flux. Using this chamber, background soil mercury flux averaged between 2 and 7 ng m^-2 hr^-1 over forest soils, and between 12 and 45 ng m^-2 hr^-1 over open, field soil. Spatial heterogeneity of soil mercury flux at duplicate plots co-located within 2 m was small but significant, differing by 20-50%. Elevated mercury emission over field soil occurred in the presence of direct sunlight at the open field sites. Solar radiation, soil temperature and soil moisture were all significant factors affecting mercury emission from soil. Solar radiation affected the reduction of naturally occurring, inorganic soil mercury compounds to volatile elemental mercury (Hg^o). We estimate that background soil accounts for the gross emission of ~10⁹ g yr^-1 of Hg^o to the atmosphere, with approximately two-thirds of this total from sunlight-exposed soil and the remainder from forest and other shaded-soil ecosystems.

Teflon Chamber for Hg Flux Measurements

Carpi, A., Lindberg, S.E. (1997) "Sunlight-Mediated Emission of Elemental Mercury from Soil Amended with Municipal Sewage Sludge," Environmental Science & Technology 31(7):2085-2091.

Hourly Hgo emissions from a sludge amended soil plot over 24-hrs. Hgo emissions were more strongly correlated with solar radiation than soil temperature. Peak background soil Hgo emissions at the same site were < 25 ng m-2 hr-1.

Abstract. We studied the fate and atmospheric emission of mercury (Hg) from soil amended with municipal sewage sludge using a Teflon dynamic flux chamber. A sunlight-mediated, in situ reduction of oxidized Hg to volatile elemental mercury (Hg^o) resulted in the atmospheric transport of Hg from land-applied sludge. The reduction of oxidized Hg to Hg^o occurred in a shallow, surface layer of soil (<0.5 cm), where light penetration was possible. Sludge application increased soil Hg^o emission by 1 - 2 orders of magnitude, to a daily average emissions rate of ~100 ng m^-2 hr^-1 greater than background. In the United States and Europe, municipal sewage sludge application to land may be responsible for the flux of ~5 x 10⁶ g yr^-1 of Hg^o to the atmosphere. Considering that municipal sewage sludge is used extensively as a soil amendment worldwide, the land application of sewage sludge warrants further study as a global source of atmospheric Hg. This research calls into question the stability of any land application of Hg-contaminated materials; all surface application of Hg waste represents a potential source of atmospheric Hg^o.

Carpi, A., Lindberg, S.E., Prestbo, E.M., Bloom, N.S. (1997) "Methyl Mercury Contamination and Emission to the Atmosphere from Soil Amended with Municipal Sewage Sludge," Journal of Environmental Quality 26(6):1650-1655.

In an effort to identify the effect of municipal sewage sludge application on mercury (Hg) concentrations in soil, we studied the contamination of sludge-amended soil with inorganic and methyl Hg and the emission of these contaminants to the atmosphere using a Teflon dynamic flux chamber. The routine application of municipal sewage sludge to cropland significantly increased both total and methyl Hg in surface soil from 80 to 6100 µg kg^-1 and 0.3 to 8.3 µg kg^-1, respectively. Both inorganic and methyl Hg were transported from the sludge/soil matrix to the environment by emission to the atmosphere, however, there was no indication of Hg transport in limited soil water lysimeter experiments. Our data from soil amended with municipal sewage sludge represent the first quantitatively measured terrestrial source of methyl mercury (MeHg) to the atmosphere. Sludge-amended soil emitted an average of 12 to 24 pg m^-2 h^-1 of monomethyl Hg and ~100 ng m^-2 h^-1 of elemental mercury (Hg^o) to the atmosphere. A simple dispersion model suggests that sludge-amended soil may increase regional atmospheric MeHg concentrations by ~5%. These data highlight the need for further research to quantify the transport of Hg from sludge-amended soil and identify the sources of MeHg in the atmosphere.

Daily average fluxes of Hgo (blue) and MeHg (red) from soil at 2 background forest sites, 1 sludge-amended forest site, and one sludge-amended open- field site in Oak Ridge, Tennessee, USA. Elevated fluxes over the open-field site were more highly correlated with solar radiation than soil temperature.

Carpi, A. (1997) "Mercury from Combustion Sources: A Review of the Chemical Species Emitted and Their Transport in the Atmosphere," Water, Air & Soil Pollution 98(3/4):241-254.

Abstract. Different species of mercury have different physical/chemical properties and thus behave quite differently in air pollution control equipment and in the atmosphere. In general, emissions of mercury from coal combustion sources are approximately 20-50% elemental mercury [Hg^o] and 50-80% divalent mercury [Hg(II)], which may be predominantly HgCl₂. Emissions of mercury from waste incinerators are approximately 10-20% Hg^o and 75-85% Hg(II). The partitioning of mercury in flue gas between the elemental and divalent forms may be dependent on the concentration of particulate carbon, HCl and other pollutants in the stack emissions. The emission of mercury from combustion facilities depends on the species in the exhaust stream and the type of air pollution control equipment used at the source. Air pollution control equipment for mercury removal at combustion facilities includes activated carbon injection, sodium sulfide injection and wet lime/limestone flue gas desulfurization.
While Hg(II) is water-soluble and may be removed from the atmosphere by wet and dry deposition close to combustion sources, the combination of a high vapor pressure and low water-solubility facilitate the long-range transport of Hg^o in the atmosphere. Background mercury in the atmosphere is predominantly Hg^o. Elemental mercury is eventually removed from the atmosphere by dry deposition onto surfaces and by wet deposition after oxidation to water-soluble, divalent mercury.

Carpi, A., Ditz, D.W., Weinstein, L.H. (1994) "Bioaccumulation of Mercury by Sphagnum Moss Near a Municipal Solid Waste Incinerator," Feature Article - Journal of the Air and Waste Management Association, 44(5):669-672.

Airborne mercury accumulation in Sphagnum moss
exposed around a municipal solid waste incinerator in
northern New Jersey.

Abstract. The Clean Air Act Amendments of 1990 and other recent regulatory actions highlight the importance of mercury from municipal solid waste (MSW) incinerators. In this field experiment, moss samplers deployed around a modern MSW incinerator showed elevated concentrations of mercury over samples exposed at a distance from the facility. These results suggest that a local pattern of airborne mercury affects the accumulation of the metal in biological media. The significance of local mercury accumulation, demonstrated by this research, is an important factor to consider in human and ecological health risk assessment.
Sphagnum moss (Sphagnum spp.) and Italian ryegrass (Lolium multiflorum Lam.) were used as biological monitors of atmospheric mercury around a municipal solid waste incinerator in rural New Jersey. Moss and grass samples were exposed according to standardized techniques at sixteen sites within 5 km of the incinerator (WCRRF). One remote site was monitored to establish background field accumulation. Duplicate and control monitors were used for quality assurance. In all cases, mercury concentrations in moss exceeded those in grass. Mercury accumulation by moss exhibited a spatial pattern consistent with a local source of pollution, considering wind and precipitation (See Figure). Total mercury in moss exposed at sites within 1.7 km of the incinerator averaged 206 ppb while samples exposed at greater distances from the facility averaged 126 ppb.

Opsomer, J.D., Agras, J., Carpi, A., Rodriques, G. (1995) "An Application of Locally Weighted Regression to Airborne Mercury Deposition Around an Incinerator Site," Environmetrics, 6:205-219.

Abstract. In this paper the deposition of mercury around an incinerator site is modeled using a non-parametric technique, locally weighted least squares regression. We begin by summarizing current theory on how multivariate locally weighted linear regression can be used to generate a regression surface and to construct approximate F-tests. We detail a simple implementation of the method that does not involve an adaptive bandwidth. This method is then applied to data on mercury accumulation in moss samples around an incinerator site, a situation where parametric modeling is not appropriate because of the small sample size and the presence of many potential covariates. The predicted regression surfaces are displayed using different bandwidth choices and suggest that the incinerator indeed affects the spatial distribution of mercury in the immediate vicinity of the incinerator (See Figures below). Approximate F-tests indicate that this effect is statistically significant at the 10% level only after the moss samples have been oven-dried. A potential explanation for this finding based on the relative volatility of different mercury species is discussed.

Predicted regression surface of mercury accumulation in undried Sphagnum moss (above).

Predicted regression surface of mercury accumulation in oven-dried Sphagnum moss.

Carpi, A., Mikhailova, Y. (2003) “The Visionlearning Project: Evaluating the Design and Effectiveness of Interdisciplinary Science Web Content,” J. College Science Teaching 23(1):12-15.

Abstract. Although the proliferation of teaching resources on the Internet is extensive, little is known about the use or utility of these materials. The Visionlearning project (http://www.visionlearning.com) is a multi-year effort to design and evaluate Web-based interdisciplinary science teaching resources. The Visionlearning resources are modular in nature and integrate text, simulations, news, history and interactive exercises to present a comprehensive overview of scientific concepts. Students using these resources in a traditional college science course scored significantly higher on a standardized assessment quiz than students who used a printed textbook. Those students who reported frequent use of the Web site scored better than their classmates who reported less frequent use.

Table: Evaluation of the Visionlearning Modules – Student Scores on a Comprehension Quiz

Mean score by section ± 95% CI	n	Treatment Group
77.0 ± 3.0	42	Sections using Visionlearning modules.
76.3 ± 3.9	73
77.8 ± 3.3	60
61.0 ± 4.7	58	Sections using a textbook and alternate web resources.
61.3 ± 2.8	54
66.1 ± 4.7	69
62.8 ± 3.5	52
54.8 ± 6.0	46	Section using textbook only

Carpi, A. (2001) “Improvements in Undergraduate Science Education Using Web-Based Instructional Modules: The Natural Science Pages,” J. Chemical Education 78(12):1709.

Abstract. Despite the rush to place educational material online, little quantitative data exists on the value of Web-based course content. In 1998, the author created a content-rich Web site (The Natural Science Pages http://web.jjay.cuny.edu/~acarpi/NSC/index.htm) to enhance science pedagogy in a required, interdisciplinary, non-major science course at John Jay College. Prior to the launch of this site, the large class size (>150) and diverse student body had presented challenges in science instruction. Since launch, the site has proven overwhelmingly successful at enhancing science comprehension. Student performance on standard exams has been substantially higher in two semesters since launch compared to one semester before launch. The percentage of students receiving a grade of C or better in the course increased from 68% before launch to approximately 78% after launch, and course failures decreased from 8.5% before launch to <5% in two semesters after launch. Over 90% of students responding to a classroom survey felt that the Web site helped them understand the subject matter taught in the course, and approximately 70% of students responded that the Web site helped improve their grade in the course. The site also helped improve student-instructor communication in the course by increasing the number of students who posed questions to the instructor outside of class-time by 5%. Enhanced Web-content is perceived by students as an effective way to increase interest and comprehension in undergraduate science education.

Table I – Mean Examination Scores Before and After Launch of the Natural Science Pages Site

Semester	Exam 1	Exam 2	Exam 3
Fall 1997^† (n = 199)	56.0 ± 15	72.2 ± 14	69.3 ± 18
Fall 1998 (n = 264)	64.5 ± 14	70.7 ± 13	80.1 ± 12
Spring 1999 (n = 141)	67.5 ± 13	67.7 ± 13	77.7 ± 11

† Prior to the launch of the course Web site.

Publication Abstracts