Air Polution With Mercury - Study From Unep

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5.0 Tracer Gas Studies and Ventilation Rate Measurements

Clayton Group Services (2004) performed air movement studies by releasing smoke into the trailer. Very little

air movement was observed. The smoke dispersed slowly in all directions from the center of the room. Sulfur

hexafluoride tracer gas was used to identify leaks from the trailer to the outside. Air exchange rates and

ventilation rates were determined by measuring decay characteristics of carbon dioxide released into the space.The ventilation rate in the large room was 17.49 cubic feet per minute (cfm) with an air exchange rate of 0.659

air exchanges per hour, whereas the small room had a ventilation rate of 24.92 cfm with an air exchange rate of

1.67 air exchanges per hour. These results were used in the air modeling presented in Section

6.1. They reflect the conditions that existed at the time the measurements were made and, since the trailer is not

airtight, are likely to change depending on environmental conditions such as wind speed and direction.

6.0 Empirical Model for Indoor Air Mercury Emission

Several models were developed and evaluated to empirically describe indoor air mercury vapor concentrations

resulting from evaporation of an elemental mercury source. The initial evaluation was based on a simple box

model presented in Riley et al (2001), which provided an order of magnitude estimate of potential mercury vapor

exposure in a room resulting from cultural and religious practices.

The box model has the form:

CtQ

S

1 eQ t

V

(1)

where,

C(t) = concentration at time t C(t) = 0 at t=0t = time (hours)

S = rate of evaporation (micro gram per hour)

Q = air flow rate from the room (cubic meters per hour)

V = room volume (cubic meters)

The box model predicts an exponential rise in mercury vapor concentration to a final equilibrium concentration

of S/Q. The rate of exponential increase is governed by the V/Q time constant which is the number of hours per

air exchange; Riley, et al. (2001) suggest a typical value of two hours for V/Q. The authors acknowledge that

their simple model only provides an order of magnitude estimate of potential exposure because the fate and

transport

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of mercury vapor inside a house is complex and case-specific, and requires data for a variety of variables,

including adsorption and desorption characteristics.

Examination of the voluminous data obtained using Lumex and Tracker real-time mercury vapor analyzers

indicates that the simple box model does not adequately predict final equilibrium mercury concentrations.

Typically, mercury concentration rises to a maximum in the first few hours and then decreases (decays) with

time until the final equilibrium concentration is reached. The decay mechanism appears to be exponential in

nature. Several potential decay models were evaluated.

The decay model best suited for modeling mercury emission data was:

CdtCt

eDt

1S

E

Q

S

E

Q

(2)

DtDt

Ct

e 1e S

E

Q

where,

Cd(t) = decay model concentration

C(t) = box model concentration

D = exponential decay factor

E = final equilibrium concentration

This model provides a smooth transition to the final equilibrium concentration and predicts concentrations that

are always less than or equal to the conservative box model concentration (upper limit). The decay component of

the model is consistent with the observed mercury emission (concentration) decrease with time, possibly due to

oxidation of elemental mercury.

Figure 27 presents Lumex monitoring data for a 45-hour time period. The data were fit to Equation 2 using the

Sigma Stat (v2.03) statistical analysis software package to perform weighted non-linear regression. The final

equation, with an r2

= 0.998, is as follows:

Cdt7121 1e0.732 t0.345

e0.117 t0.345

1e0.117 t0.345

140

7121

The final equilibrium concentration predicted by this equation was 140 ng/m3

(0.14 Fg/m3

); this value is

reasonable based on the data in Figure 27. The t + 0.345 term (t + t0) accounts for time offset between time zero

and the start of monitoring measurements.

Table 3 presents decay model (Equation 2) non-linear regression results for several sets of mercury concentration

vs. time data (r2

range = 0.910 to 0.998). Lumex and Tracker monitoring data, box model results and decay model

calculation results are presented in Figures 27-34. The room volume was fixed at 25.37 m3

for all nonlinear

regression analyses.


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The data in Table 3 show a wide range of air exchange rate (Q/V) values (0.099 to 1.54, average = 0.68) for

the mercury monitoring data sets evaluated. The data in Table 3 are generally in agreement with the range of

mean residential air exchanges per hour (0.53 to 1.1) noted in a National Research Council report on the risk

associated with radon in drinking water (NRC, 1999), and with those (0.25-1.57) reported in a study of

residential air exchange rates in the United States (Murray et al., 1995). Fit values for the E term indicate

that the decay model final equilibrium concentration is generally 2-4 percent of the box model equilibrium

value. The fit parameters for the August 19, 2002 Lumex monitoring data set (see Figures 31 and 32) may be

unreliable because the time offset parameter reached the defined upper limit (0.5 hours) within the first three

iterations of the regression. The August 5, 2002 Lumex monitoring data (Figure 27) and August 7, 2002

Tracker monitoring data (Figure 28) are from the same 45-hour time frame. Regression results for Q, D, and E

terms are in good agreement for the two monitoring data sets. There are a number of individual Tracker or

Lumex readings in Figures 27-34 that are lower than the adjacent readings on the figures. These readings are

normal and occur during automatic monitoring instrument zero adjustments, and do not reflect actual

measured concentrations.

Overall, this decay model (Equation 2) is adequate for describing elemental mercury emissions provided all

environmental factors are stable (constant). The factors include temperature, ambient pressure, air exchange

rate, and electrostatic effects. In addition, the elemental mercury source must be undisturbed. It is highly

unlikely that all these conditions are met during ritualistic uses of mercury. This is evident from the observed

bumps in the mercury concentration vs. time data sets (Figures 27-34).

The empirical decay model cannot predict the final equilibrium concentration due to the lack of data for

elemental mercury oxidation as a function of time, temperature, etc. Mercury monitoring results indicate that

the final equilibrium concentration is typically less than 5 percent of the simple box model predicted

concentration. The final concentration appears to be reached after 50-60 hours of stable, undisturbed elemental

mercury vaporization.

Figure 35 presents mercury concentration vs. time data when the mercury container was shaken for the first 16

hours. The box model appears to accurately predict mercury concentration for the first nine hours (Figure 36)

before mercury emission rate decay begins. Figure 37 shows the final model with a rate decay time offset of

9.04 hours. The final model, with an r2

= 0.957, is:

CtBox ModelBM

23.49

t0.137

7.322

1 e

25.37

0.926 t0.137

7.322 1 e t9.04 hours

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0.0378

0.0378

0.124 t9.041

CtBM

e

1

7.322

7.322

0.124 t9.041

BMe 1 0.0051630.005163t9.04 hourswhere, S/Q = S/23.49 = 7.322; therefore, S = 172 g/hour and the final equilibrium concentration is

0.038g/m3

.

6.1 Model for Predicting Average Indoor Air Mercury Concentration

Additional studies were carried out to develop a simple model to predict average mercury vapor

concentrations in indoor air based on average emission over various

Table 4 presents mercury emission rates based on weight loss from mercury beads of different

diameter. Figures 38 and 39 present Tracker mercury concentration (twohour average) vs. time data for

nominal 0.5 cm beads. Figure 40 presents the nonlinear regression analysis for the nominal 0.5 cm bead

average mercury emission rate in micro gram per hour per square centimeter (g/hr/cm2

) vs. time data

(22-864 hours). Figure 41 includes emission rate data for nominal 0.5 cm beads and other bead sizes.Total bead surface areas were based on the effective bead diameter, which was calculated assuming a


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spherical bead with weight equal to the starting weight divided by the number of beads and density of

13.6 g/cm3

. The beads tend to flatten and spread out on the surface upon which they rest, therefore, the

bead active emitting surface area is less than 100 percent. The fraction of bead surface area available

for

time

inte

rvals.

emission depends upon several factors including bead diameter, resting surface roughness, and surface

tension. The bead active surface area for emission was assumed to be 50 percent for this study. The

final model (Equation 3) can be used to predict average emission rate, S , for 22-864 hours exposure

time (r2

= 0.943).

S' avgg/ hr/ cm2

96.947 e 0.0188hours 0.0000033 hours0.0968(3)

The nominal 0.5 cm data in the first two sections of Table 4 (first 11 data sets) were used to determine model

parameters in Equation 3; the data in the last set was not

shellfish (e.g., tribal and other subsistence fishers and their families who rely heavily on locally caught fish for

the majority of their diet).

Although people are exposed to methylmercury via the dietary route, there are also some non-dietary sourcesof mercury exposure. Many consumers are not aware that mercury has been used for years in common

household products such as thermostats. Releases from the manufacture of mercury-containing products and

inappropriate disposal of these products have contributed to mercury entering the environment and ultimately

the food chain. Misuse of or accidental breakage of some products can create indoor air health risks and expose

consumers to dangerous levels of mercury. In addition, certain cultural or religious uses of mercury may also

result in harmful mercury exposure. The number of individuals exposed in the U.S. in this way is very small.

The Agency will make it a priority to provide consumers with reliable risk information about mercury

exposure so that they can make informed choices about the fish they eat and the products they use.

Progress to date. EPA has directed most of its mercury risk communication activities toward raisingawareness about dietary practices. The FDA-EPA national advisory,

What You Need to Know About Mercury in Fish and Shellfish, provides advice for women who might become

pregnant; women who are pregnant; nursing mothers; and young children.2This advisory represents the first

time FDA and EPA have combined their advice into a single uniform advisory. During the summer and fall of

2004, the two agencies distrib


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IV. Communicating to the Public about Mercury Exposure Risks - 49


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uted brochures about the advisory to approximately 200,000 medical providers in the U.S.

In September 2005, EPA sponsored the Eighth Annual National Forum on Contaminants in Fish

(Fish Forum). The forum provided an opportunity for people who have an interest in the subject

of advisories, from both the public and private sectors, to discuss scientific and policy issues, risks

and benefits, and communication strategies associated with exposure to chemical contaminants insport- and subsistence-caught fish and shellfish. In September 2005, the 13th straight year, EPA

released its National Listing of Fish Advisories, a summary of information on locally-issued fish

advisories and safe-eating guidelines.3

This information is provided to EPA annually by states,

territories, and tribes.

States and tribes issue fish consumption advisories if elevated concentrations of chemicals such as

mercury are found in local fish. States monitor their waters by sampling fish tissue for persistent

pollutants that bioaccumulate. States issue their advisories and guidelines voluntarily and have

flexibility in what criteria they use and how the data are collected. As a result, there are significant

variations in the number of waters tested, the pollutants tested for, and the threshold for issuing

advisories. Based on self-reporting, the national trend is for states to monitor different waters each

year, generally without retesting waters monitored in previous years.4

As new waters are tested and

results are added to previous years findings, the number of fish advisories continues to rise. EPA

makes information on the fish advisories, as well as Fish Forum proceedings, easily accessible to the

public on its website.

Although most of EPAs risk communication efforts have been directed to increasing awareness of

mercury in the food chain, the Agency has also investigated non-dietary sources of mercury

exposure about which the public should be aware. Risk communication has been conducted in

conjunction with mercury reduction activities, such as school clean-outs or thermometer collection

programs. In many cases, critical mercury outreach to schools and communities would not

otherwise occur without EPA assistance. For example, EPAs Region 6 has identified a particularneed for such support in communities on the U.S./Mexico border.

EPAs national efforts on mercury risk communication have been aimed at making information

widely available to the public and at co-sponsoring national conferences that bring together people

from across the country to share information on mercury risk communication. A unique exposure

concern is raised by ritualistic use of mercury in certain cultural communities. For this reason, in

January 1999,

The largest source of emissions to the atmosphere is currentlycoal fi red power stations, however, the widespread use ofmercury in dental amalgam means that in the future, crematoriacould become the most signifi cant source. Hospitals withmedical waste incinerators are also a major contributor to themercury problem, and although emissions are decreasing asthe number of medical waste incinerators is reduced, there isconcern within the health community that the use of mercuryin healthcare products is exposing patients and other vulnerablegroups. The chlor-alkali industry, the biggest single user


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of mercury in Europe, has released many tonnes of mercuryto the aquatic environment over the years, and contributed tofi sh contamination52.Approximately 70% of environmental mercury now comesfrom human activities including a variety of industrial processes;coal burning, incineration or disposal of mercury-containingproducts, the use of mercury for chlorine productionin the chlor-alkali industry, production of zinc, steel and othermetals; cement production, mining and product recycling.Mercury is used in a variety of industrial, consumer and medicalproducts.It is also released into the environment through natural phenomena(volcanoes, degradation of minerals or evaporationfrom soils) and manmade processes.PRODUCT EXAMPLES AT A GLANCEg:

fl uorescent light bulbs and batteries,medical devices: thermometers, blood pressureinstruments (sphygmomanometers),

laboratory chemicals, preservatives in some vaccinesand pharmaceuticals, and in dental amalgams

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.various temperature and moisture measurement andsensing devices (barometers, hydrometers, fl amesensors).gA very detailed list of mercury use in products is available, see: TheEuropean Commission, DG Enterprise. Risks to Health and the EnvironmentRelated to the Use of Mercury Products. Prepared by Risk & Policy AnalystsLimited, Norfolk. J372/Merkury. August 2002. Annex 3.

Hospital waste can contribute to

mercury emissions21Stay Healthy, Stop Mercurycampaign

Table 2. USE, EXPOSURE ROUTES AND TOXICITY OF MERCURY AND ITS COMPOUNDS54 55MercuryForm

Elemental (Hgo) Inorganic(mercury salts)(Hg1+)Organic- methylmercury (CH3Hg-)Organic ethyl mercury(C2H5Hg-)Organic phenyl mercury(C6H5Hg-)Main Use Dental fi llings (amalgam isa mix of mercury and other

metals like Ag, Sn, Cu, In, Zn)Medicines,Cosmetics(used as apreservative)No intentional uses,when depositedinto water, mercuryis transformed intomethylmercury by


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micro organismsand bacteria.Vaccines (thepreservativethimerosalis 49% ethylmercuryFungicide,bactericideOther uses GoldminingChloralkali plantsProducts (batteries, switches,fl uorescent bulbs, measuringand control devices eg.thermostats)Medical devices (thermometers,gastrointestinal tubes,sphygmomanometers)Santoria and other ethnic andreligious rituals

Disinfectants andanti-microbialsElectricalequipmentPhotographySource ofexposureHospital spills eg. brokenthermometersDental amalgamHome spillsChildren playing withquicksilver used in ethnic/

religious ritualsFish consumption(the fi sh haveingested methylmercury and it is intheir muscle tissue)Route ofexposureandabsorptionrateInhalation: 80% absorbedIngestion: 0.01% absorption

Dermal: minimal absorptionIngestion: ~10%absorbedDermal: lethaldoses can beabsorbedInhalational: wellabsorbedIngestion: 90-100% absorbed


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Injection: 100%absorbedIngestion: 80-100% absorbedDermal: seesaltsToxicity -primaryLungs, Skin, Eyes, Gingiva Kidneys, GastrointestinaltractCentral nervoussystemunder study KidneysToxicity -secondaryCentral nervous system,KidneysCentral NervoussystemCardio-vascular

under studyCentral nervoussystemTransport inbodyCrosses blood- brain barrierCrosses the placentaFound in breastmilkDoes not easilyenter the brainor cross theplacentaCrosses blood-brain

barrierCrosses theplacentaFound in breastmilkCrosses bloodbrainbarrierCrosses theplacentaFound inbreastmilkNOTE: Dose and Timing of Exposure are not refl ected in this table

Air Polution With Mercury - Study From Unep

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