Particle Size Distribution

Lake Pontchartrain

Figure 2. Particle size distribution of Lake Pontchartrain and in-home sediments. Data from references (5, 10).

Lake Pontchartrain

Home 1

Home 2

Figure 2. Particle size distribution of Lake Pontchartrain and in-home sediments. Data from references (5, 10).

are nearly 20% sand (particles having diameter greater than 63 |im), whereas for the in-home sediments the maximum sand content is between 2 and 8 %.

Sediment geochemistry is important because the types of particles present in a sediment have great influence over both the type and amounts of contaminants which may be found. Silt and clay particles have high specific surface areas, and large quantities of adsorption sites on the mineral surface. These adsorption sites can serve as hosts for metal and organic pollutants, and it has been shown by many researchers that the degree of contamination of a sediment increases with increasing silt and clay content (18-20). Sediment organic matter also plays a role in sequestering pollutants from floodwaters into sediment material. Inhome sediments were found to have organic carbon contents ranging from 7-9% (10); volatile and semi-volatile pollutants may partition into the sediment organic matter, in addition to adsorbing to active sites on the mineral surfaces.

The sediment geochemistry analysis has important consequences for the overall post-Katrina environmental analysis. Because the in-home sediments are overwhelmingly dominated by fine particles (silts and clays), whereas coarser particles (sand) are expected to be winnowed out on the exterior, the potential exists for in-home sediments to be more contaminated than their exterior counterparts. This would have important implications for exposure to returning residents and recovery workers. Sediment pollutant concentrations will be explored more fully in the following section.

In-Home Sediment Contaminants

Metals

Average sediment metal loadings for the two flooded homes are given in Table II. Of the twenty metals analyzed, four were detected in high concentrations, including arsenic, cadmium, lead, and vanadium.

Table II. Average metal concentrations from sediment inside two flooded homes.

Home 1

Home 2

Arsenic

66

194

Cadmium

38!

104

Lead

274

1500

Vanadium

64

45

Note: Units are mg/kg dry sediment Source: Data from reference (10).

Note: Units are mg/kg dry sediment Source: Data from reference (10).

Arsenic, cadmium and lead sediment concentrations exceed their EPA soil screening standards by 1.5 - 10 times. Compared with an exterior sediment sample taken from between the two homes, arsenic concentrations are two times higher, cadmium concentrations nearly ten times higher, and lead concentrations four times higher than the exterior sample (21). One of the primary reasons for the elevation of the in-home samples to the exterior ones must be attributed to the sediment particle size geochemistry as described earlier.

Comparison with New Orleans soil background concentrations from pre-Katrina studies shows that for arsenic, cadmium, and vanadium, the in-home, flood-deposited sediments are more highly contaminated compared to previous levels of exposure. Average indoor arsenic and vanadium concentrations are nearly four times greater, and cadmium nearly fifty times greater than pre-Katrina outdoor soil background concentrations (10, 22). Lead concentrations were in the range of previously measured soil concentrations, due largely to the fact that New Orleans soils historically contain very large quantities of lead (7, 8, 23, 24).

High loadings of arsenic, cadmium, and lead may pose a direct risk to returning residents, first responders, and recovery workers. Persons may be exposed to these contaminants while trying to recover items from damaged homes, or while trying to clean up and renovate the homes. Based on the above data, it is also evident that "safety" warnings and bulletins based solely on measured exterior sediment concentrations may under-predict the real exposure of toxic metals to returning residents.

Organics

Selected results of the sediment organics analysis, along with modeling results for the vapor-phase, aerosolized mold spores, and mold film are shown in Table III.

Types of compounds detected include the alkanes from motor vehicle fuel, aldehydes, esters from plasticizers, organic acids, pesticides from agricultural runoff and termite control, and PAHs and volatiles from fuels. In particular, the pesticides and PAH fluoranthene are detected in high concentrations. The concentrations of chlordane and dieldrin, two common pesticides, are both 100 times greater than the EPA soil regulatory standard (II). The concentration of the PAH fluoranthene is nearly 20 times that detected in an outdoor sample located between the two flooded homes (21). These results, combined with the comparison of indoor and outdoor sediment metal concentrations, lends further credence to the theory that in-home sediment contaminants may be present at higher loadings as a result of the particle winnowing process. The high loadings of pesticides relative to their EPA screening standard, along with the large increase in fluoranthene concentration compared to the exterior sample again reiterate the fact that advisories to returning residents based solely on exterior sampling may under-predict the actual exposure to certain hazardous pollutants.

Predicted Vapor-Phase Contaminants

Predicted results for the indoor vapor-phase concentrations were also shown in Table III. The results show that some of the aldehydes, alkanes, esters, pesticides, and volatiles may be present in significant concentrations in the vapor-phase.

The volatile trimethyl benzenes have very high vapor pressures, and their appearance in significant quantities in the vapor space inside the home is expected. Organic acids are also common vapor-phase pollutants (25). Potentially high concentrations of the pesticide chlordane may represent a particular area of concern for returning residents, as long-term inhalation exposure can lead to chronic health conditions (26).

Table III. Measured and predicted concentrations for selected pollutants across multiple indoor phases.

Compound Measured Vapor Mold Mold

Sediment Phase Aerosol Film

Home Home Home Home Home Home Home Home

/

2

1

2

/

2

1

2

Chlordane

280

BDL

76.4

BDL

267

BDL

32,200

BDL

Dieldrin

3.0

BDL

1.4

BDL

0.8

BDL

93.9

BDL

Fluoranthene

35.6

46.5

6.5

6.9

20.7

21.9

2490

2650

Heptadecane

3.3

2.3

1320

1290

1.7

3.7

207

452

Nonanal

BDL

7.8

BDL

31,300

BDL

8.2

BDL

985

Oleic Acid

338

697

69.5

67.9

Phthalic

BDL

292

BDL

260

BDL

65.1

BDL

7860

anhydride

Tetracosane

105

37.1

1.6

1.5

0.8

2.2

93.9

269

Trimethyl

3.5

BDL

15,400

BDL

1.1

BDL

129

BDL

benzenes

Note: BDL = below detection limit in sediments; mold model unable to be processed for organic acids Source: Data from references (10, 12)

Note: BDL = below detection limit in sediments; mold model unable to be processed for organic acids Source: Data from references (10, 12)

Sediment moisture content plays a key role in the distribution of pollutants between the sediment and vapor phases, because water competes with organic species for adsorption sites on clay mineral surfaces. A damp or saturated sediment can force volatile and semi-volatile organic molecules into the vapor phase, where they may function as an inhalation exposure source to persons entering the flood-damaged homes (27, 28). Therefore, the worst-case wet sediment modeling approach employed herein is useful because it predicts a maximum possible indoor vapor phase concentration, and sets an upper limit on the concentrations to which residents and recovery workers may have been exposed to volatile and semi-volatile pollutants in the gas phase.

Predicted Aerosolized Mold Spore Contaminants

Results of the modeling work for aerosolized mold spores, also shown in Table III, reveal that some esters, pesticides, and the PAH fluoranthene may partition into the aerosol phase in appreciable concentrations. These results are significant because they demonstrate that the aerosolized mold spores, present in nearly every flooded home in New Orleans following Hurricane Katrina, can act as a partitioning medium for certain classes of pollutants from the vapor phase.

Mold spore concentrations inside flooded homes in excess of 500,000 spores/m3 have been measured (29). It is clear that at these extremely high concentrations, inhalation of spores by returning residents and recovery workers is unavoidable. The N-95 respirators recommended by many agencies have been shown to have little effect against spores (30). If the spores can also contain organic pollutants, then the total inhalation exposure to certain classes of contaminants will be the sum of the vapor-phase and aerosol-associated masses. Exposure assessments which only accounted for vapor-phase pollutants may then under-predict the real amount of exposure.

The high indoor mold spore concentrations discussed above will have the effect of creating a highly concentrated aerosol phase inside the flooded homes. Because the mold spores are comprised mainly of water, organic, and biological components (31), it is completely plausible to believe that mold can act as a partitioning medium for volatile and semi-volatile species in the gas phase. The idea of mold spores acting as a sink for organic pollutants in flooded homes has not previously been considered, yet represents a key piece of the total environmental picture in post-Katrina New Orleans. Modeling results indicate that many of the alkanes may also be present in considerable amounts in the aerosolized mold spores (12). This is somewhat surprising given the low vapor-phase concentrations of the alkanes. However, many of the organic species comprising the mold spores, such as lignin and other long-chain hydrocarbons, are chemically very similar to the alkanes, and as such they may have a special affinity for the mold. The pesticide chlordane, fluoranthene, a carcinogenic PAH, and the volatile benzene derivatives also show potentially high loadings in the aerosol phase. These results are especially important because chlordane and the trimethyl benzenes also showed the potential for high vapor-phase concentrations; therefore their presence in the aerosol phase could lead to a very high total inhalation exposure of these compounds. Overall, modeling results for the aerosolized mold spores suggest that their presence should not be ignored in understanding the total chemodynamic behavior of indoor contaminants from flooded homes. For specific compound classes, the mold spores may also contribute substantially to the total inhalation exposure to toxic materials.

Predicted Mold Film Contaminants

Compared to the aerosolized mold spores where the primary means of exposure will be through inhalation, mold films growing on walls and other interior surfaces represent exposure concerns through dermal contact, as well as present issues to be considered in the disposal of housing debris. Predicted mold film concentrations were also provided in Table III.

Modeling results indicate that pesticides and esters may be the most significant pollutants in this phase. When destroyed homes are torn down or gutted, contaminated debris including drywall, upholstery, furniture, and other items that may contain a mold film are often disposed of in landfills or other waste disposal facilities. Pesticides and esters, which may be present in high concentrations in the mold film, are thus also introduced to the landfills or incinerators. Careful monitoring of effluent streams and by-products of these facilities should be conducted to ensure that no hazardous materials are leaving the site.

Overall Mass Distribution

The summary results of the overall mass distribution model are shown in Table IV. The mass distribution model shows which classes of pollutants may be the most important in each specific phase, giving a "snapshot" view of the distribution of contaminants across multiple phases inside New Orleans flooded homes.

Results show that the sediment is dominated by alkanes and organic acids, the vapor-phase by aldehydes, volatiles, and organic acids, and the mold phases (both film and aerosolized spores) by pesticides, esters, and PAH. Several important exposure conclusions can be drawn based on the mass distribution. First, organic acids are prevalent in both the sediment and vapor-phases, and thus may be significant in terms of both dermal and inhalation exposure. Second, because pesticides and esters are large contributors to both the vapor and mold phases, their additive contribution to respirable vapors and aerosolized mold spores may be very significant, and neglecting the aerosolized mold phase may under-predict the total exposure to these chemicals.

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