Decisions about rebuilding are based more on the potential for reflooding than on the overall health of the New Orleans area.
When Hurricane Katrina flooded the city of New Orleans, one of many concerns in its wake was contamination. Several chemical plants, petroleum refining facilities, and contaminated sites, including Superfund sites, were covered by floodwaters. In addition, hundreds of commercial establishments, such as service stations, pest control businesses, and dry cleaners, may have released potentially hazardous chemicals into the floodwaters. Figure 1 (see PDF version for figures) shows potential petroleum-related release points, including refineries, oil and gas wells, and service stations near the city. Figure 2 shows the major hazardous-materials storage locations, Superfund sites, and Toxic Release Inventory reporting facilities.
Adding to the potential sources of toxics and environmental contaminants are metal-contaminated soils typical of old urban areas and construction lumber preserved with creosote, pentachlorophenol, and arsenic. Compounding these concerns is the presence of hazardous chemicals commonly stored in households and the fuel and motor oil in approximately 400,000 flooded automobiles. Uncontrolled biological wastes from both human and animal sources also contributed to the pollutant burden in the city.
In the confusion immediately after the flooding, the amount of contamination was not known. Oil slicks near some service stations and flooded automobiles and wastes floating or suspended in floodwaters provided clear evidence of some environmental releases. A 250,000-barrel above-ground storage tank at the Murphy Oil USA Meraux Refinery in St. Bernard Parish southeast of the downtown area was dislodged and lifted by the floodwaters, spilling approximately 25,000 barrels (more than one million gallons) of crude oil and impacting a one square mile area containing approximately 1,700 homes (EPA, 2005c).
Several efforts were made during and after the flooding to monitor and quantify chemical and biological contamination and assess exposures to, and risks from, toxics and contaminants. Federal agencies, including the Environmental Protection Agency (EPA) and National Oceanographic and Atmospheric Administration, collected environmental samples both in New Orleans and from the surrounding area impacted by Hurricane Katrina. Initial concerns in the city were focused on acute exposures for stranded residents and relief workers. Subsequent efforts have been focused on acute exposures for returning residents and initial assessments of chronic exposures. The results of independent sampling have been reported by Pardue et al. (2005), Presley et al. (2006), and the National Resources Defense Council (NRDC, 2005b).
Studies to date have generally painted a consistent picture of contamination in the air, water, and soils and sediments of New Orleans both during and after the flood. Thus, they provide a reasonable characterization of the general quality of the floodwaters and the soils and sediments that remain. The data are relatively sparse, however, and therefore may not fully characterize localized problems.
Regulatory agencies typically assess risk on the basis of 95-percent upper confidence limits in concentrations of media to which exposure occurs. However, for the sake of simplicity and because of the difficulty in characterizing contamination from sparse data, we focus on maximum observed concentrations. Our goal is to summarize key results from the available data to suggest the general character of the toxics and contaminant exposure during and after the flooding and to put in perspective findings for the rebuilding of New Orleans.
Exposures during Flooding
Floodwaters were present in the city from the passage of the storm on August 29, 2005, until the city was declared dewatered by the U.S. Army Corps of Engineers on October 11. Sampling showed elevated levels of inorganic and organic contaminants and biological constituents, including pathogens. The level of inorganic contaminants was generally low, even compared to drinking water standards. Presley et al. (2006) found no floodwater samples with concentrations higher than those designated for drinking water or acute and chronic threshold concentrations. Pardue et al. (2005) noted consistently high levels of arsenic in the floodwaters (mean of 30 ?g/L compared to a maximum contaminant level in drinking water of 10 ?g/L). Drinking water standards, however, are not an appropriate indicator of water quality for floodwaters because they are based on the assumption that a person drinks two liters of water every day for 70 years, whereas much less floodwater is ingested or absorbed through dermal exposure.
Organic constituents in floodwaters were also at relatively low concentrations. This observation was initially met with some surprise because of the evident oil and hydrocarbon fuel spills in many locations. Soluble petroleum oils and fuel constituents, such as benzene, however, are typically volatile, leading to rapid release to the air; less-soluble constituents partition to sediments left behind by the floodwaters. EPA concluded that inorganic and organic chemical concentrations in floodwater were generally below levels of concern for short-term (90 days) dermal contact and incidental ingestion (EPA, 2005b).
Bacterial contamination in the floodwaters was a source of great concern. Median concentrations of fecal coliform of approximately 104 MPN/100 mL were detected in the floodwaters (Pardue et al., 2005). This can be compared to a water quality standard for primary contact of 200 MPN/100 mL. The detection of human pathogens, such as Aeromonas spp., at concentrations on the order of 107 CFU/mL at two locations in the downtown area, raised even greater concern (Presley et al., 2006). Members of the genus Aeromonas, which have been associated with diarrhea and wound infections in humans (Janda and Duffey, 1988), have also frequently been isolated from soils and fresh water.
were similar in character
to normal storm waters.
Contaminants in Lake Pontchartrain
Another major concern is the immediate and long-term impacts of the discharge of floodwaters into Lake Pontchartrain. From September 6 to October 11, floodwaters, which had largely originated in the lake, were returned to their source. Lake Pontchartrain is a brackish, shallow lake with a surface area of approximately 1,630 km2 and an average depth of about 4 m; there is an active commercial fishery on the lake. Pardue et al. (2005) detected low levels of dissolved oxygen in floodwaters and in discharged water, which likely resulted in low oxygen levels in the immediate vicinity of the discharge point but had a minimal impact on the lake as a whole. Similarly, the generally low levels of inorganic and organic contaminants in the floodwaters were unlikely to have significant impacts on Lake Pontchartrain.
The sediments at the mouth of the discharge canals contained some contaminants prior to the flooding as the result of normal wastewater and stormwater discharges from the city. The Katrina floodwaters were similar in character, although significantly larger in volume, to the normal stormwaters discharged into the lake (EPA, 2005b). Bacterial contamination of the discharge waters was typically an order of magnitude higher than prior to discharge (as measured by fecal coliform concentration). But in more than 100 samples collected by EPA in September and October, bacterial levels in the lake were within recreational limits (EPA, 2005b).
In summary, with the possible exception of biological pathogens, direct exposure to floodwaters either in the city or in Lake Pontchartrain appeared likely to have minimal toxic or contaminant impacts.
Exposures to Post-Flooding Soil and Sediment
Although floodwaters were removed from the city by October 11, 2005, their legacy of contaminated soils, sediments, debris, and houses remains. In addition, sediment mobilized from storm surge through Lake Pontchartrain and the Mississippi River Gulf Outlet/Industrial Canal was deposited in the city. Additional sampling was done to assess the concentrations of chemical and biological contaminants in these media. Presley et al. (2006) found several inorganic constituents (arsenic, iron, and lead) and organic constituents (mostly polycyclic aromatic hydrocarbons [PAHs]) in sediments from New Orleans that exceeded EPA Region 6 Human Health Specific Screening Levels for soils, which are used to evaluate the “relative environmental concern for a site or set of environmental data. The values are not regulatory, but are derived using equations from EPA guidance and commonly used defaults” (EPA, 2005a).
The Screening Levels, which are “not generated to represent action levels or cleanup levels but rather as a technical tool” (EPA, 2005a), are “chemical concentrations that correspond to fixed levels of risk (i.e., either a one-in-one million  cancer risk or a noncarcinogenic hazard quotient of one, whichever occurs at a lower concentration) in soil, air, and water,” based on assumptions of lifetime exposures to general, but not uniform, exposure values at the upper end of the range of possible exposures (EPA, 2005f).
Of the 430 sediment samples collected by EPA between September 10 and October 14, a number exceeded screening criteria of the local regulatory authority, the Louisiana Department of Environmental Quality (LDEQ Risk Evaluation/Corrective Action Program or RECAP) (LDEQ, 2005). These criteria were developed to meet objectives similar to those of the EPA Health Specific Screening Levels and are similarly derived. The constituents most often found to exceed the RECAP screening criteria were arsenic, lead, several PAHs (including benzo[a]pyrene), and diesel range organics.
On November 19 and 20, EPA resampled areas where previous sampling had indicated contaminant concentrations in excess of screening criteria and where sediment depth equaled or exceeded 0.5 inches (EPA, 2005b). Because of the complex nature of the storm surge and levee breaches and overtoppings, the amount of sediment deposited in flooded areas varied widely, and only 14 of the 145 locations had sufficient sediment depth. Three samples showed arsenic concentrations higher than 12 mg/kg (14.4–17.6 mg/kg); one sample showed benzo[a]pyrene concentration of 0.77 mg/kg; and one sample showed a concentration of diesel range organics of 2,100 mg/kg. Other samples were below applicable screening values.
Samples were also collected at specific sites where there were known or potential leaks of hazardous materials. Elevated concentrations of total petroleum hydrocarbons and a variety of crude oil-associated contaminants were observed in the vicinity of the Murphy Oil crude oil tank failure and spill, which had a clearly identifiable source and could be easily differentiated from the general flooding-related contamination. This area is being managed separately from the rest of the flooded area and is not considered further here.
EPA also collected 74 soil samples at the site of the Agriculture Street Landfill, a closed Superfund site that was flooded by Katrina. The samples were collected immediately above the geotextile liner (12 to 24 inches below ground), which was installed as part of the site remedy. All samples were analyzed for lead, which was the contaminant of concern that defined the cleanup, but none showed concentrations that exceeded the lead cleanup standard or EPA screening standards for lead. EPA concluded that the flooding did not impact the effectiveness of the remedy (EPA, 2005d).
NRDC analyzed samples for other contaminants at the Agriculture Street site and found arsenic at levels similar to those found at other New Orleans sites and a variety of high molecular weight PAHs at somewhat elevated levels (NRDC, 2005c). They ascribed the presence of the high molecular weight PAHs to leachate from the landfill, although, because of the hydrophobic nature of these compounds, they would more likely be transported by resuspended soil from the site or elsewhere. Further assessment of this area might be warranted.
has complicated post-
flooding assessments of
soils and sediments.
The presence of a pre-Katrina background of contamination has complicated the assessment of concentrations in soils and sediments. For example, background concentrations of arsenic throughout the Mississippi River Delta region of south Louisiana is on the order of 10 mg/kg (Gustavsson et al., 2001), and LDEQ has reported a background arsenic concentration of 7 mg/kg. Pre-Katrina concentrations of arsenic could be even higher in residential areas because of arsenic in lawn fertilizers (WSDA, 2001).
Lead has also long been a concern in inner city New Orleans. About 40 percent of nearly 5,000 soil samples showed lead levels in excess of 400 mg/kg (Pelley, 2006). Presley et al. (2006) found lead in excess of 400 mg/kg (405 and 642 mg/kg) in two of 12 sediment samples, consistent with the pre-Katrina observations of Mielke et al. (2004). The latter also showed elevated levels of PAHs in pre-Katrina soils of New Orleans and positive correlations between PAH levels and metal contamination.
With only 12 sediment samples collected by Presley et al., 14 that met the depth and previously detected contamination criteria by EPA in the November 19 and 20 sampling, and even fewer samples reported in other analyses, it is impossible to differentiate statistically the current observations from pre-Katrina contamination levels. Thus, except in areas impacted by specific events, such as the failure of the oil storage tank and the Superfund site, there was no general contamination of New Orleans to clearly unacceptable levels—especially with respect to acute exposures.
Evaluating risks to human
health is complicated
by the lack of clearly
Residents attempting to return to the city must be aware of the level of risk and the need for remediation prior to their return. The uniqueness of the short-term exposure pathways complicates the assessment. Not only are home owners faced with removing both wet and dry sediment from their homes and yards, but exposure to airborne hazards, such as mold and dust from these sediments, has also occurred, exacerbated by demolitions and home “gutting” activities throughout the region.
Soils and Sediments
Evaluating the risk to human health associated with contaminant levels in post-Katrina soils and sediments is complicated by the lack of clearly applicable standards, which typically apply to the risk of inhalation, or, in the case of water standards, to use-related risk (e.g., drinking water vs. recreational-use water). For soil and sediment concentrations, however, pathways of exposure may be incomplete (e.g., direct exposure to buried soil not subject to significant erosion) or variable (e.g., soil in a park vs. residential soil), or contaminants may be present in forms that are largely unavailable for uptake (e.g., metals largely associated with low-solubility metal sulfides). Therefore, screening or threshold values are being used to assess the need for soil and sediment remediation and to guide the development of cleanup standards.
Under the Louisiana RECAP standards, a site with concentrations below the levels defined on the basis of default lifetime-exposure assumptions and without site-specific exposure or availability data can be considered safe; thus, remedial action is not required. As is typical with such approaches, however, concentrations that exceed the level defined by default assumptions also may not require cleanup. “To prevent misuse of screening levels,” EPA Region 6 normally considers other factors, such as “[a]pplying screening levels to a site without adequately developing a conceptual site model that identifies relevant exposure pathways and exposure scenarios . . . [n]ot considering background concentrations when choosing screening levels . . . [using] screening levels as cleanup levels without the consideration of other relevant [remedy selection] criteria”, and “[using] screening levels as cleanup levels without verifying numbers with a toxicologist/risk assessor” (EPA, 2005a). For example, a review of the arsenic soil cleanup levels at Superfund or state sites indicates a wide range of concentrations, from background levels to hundreds of parts per million (ppm), depending on site-specific conditions (EPA, 2005e).
Under RECAP, there are two management options (in addition to using a tabulated screening level) for defining alternative concentration standards that might apply to a particular site. One option includes site-specific information with specified analytical fate and transport models and default exposure assumptions as a basis for defining concentration standards different from screening values. The other option is based on site-specific exposure and environmental fate and transport data. All site-screening approaches have a similar structure and allow for modifications so that site-specific information can be used to refine estimates of exposure and risk and inform remedial planning.
According to LDEQ policy, a total lifetime cumulative carcinogenic risk level of more than 106 may be acceptable, as long as the cumulative risk associated with residual constituent concentrations following corrective action is at or below 104 (LDEQ, 2003). Even using conservative default exposure assumptions, an arsenic concentration of approximately 40 ppm may be deemed acceptable if arsenic is the predominant contaminant.
Thus the need for remedial action at any particular site in New Orleans must be assessed on the basis of an evaluation of that site for (1) average concentrations that exceed screening values in an area where a resident or worker might be regularly exposed and (2) pathways and attenuation along routes of exposure that lead to unacceptable risk.
Even screening values based on generally conservative default assumptions may not be fully protective in all cases, however. In general, EPA, states, and the scientific community regularly reassess whether the methodologies used in the risk assessment process are adequate to protecting children and other sensitive populations, even when default exposure values are used. Currently, this question is supposed to be addressed on a case-by-case basis.
Although the sampling and analysis required for a site-specific assessment and evaluation approach can be costly, using screening levels as remedial goals could also be costly unless there is some assurance of a commensurate reduction in risk. An individual home owner can assess the contamination on his or her property, but, in the absence of government support for testing and cleanup, the responsibility and cost would fall disproportionately on the poor. Thus, home owners would naturally avoid testing. However, a generic response to potential contamination would undoubtedly lead to the destruction of property that does not pose excessive risks and would further delay the return of people to their homes.
Another concern is the presence of mold and airborne mold spores in homes. Unlike air, water, and soil contamination, there is little scientific basis for evaluating the potential effects of mold on human health or for developing risk-based action or cleanup levels. Mold counts of 50,000 spores/m3 are considered very high; spore counts as high as 650,000 spores/m3 were observed by NRDC in a home in mid-city New Orleans (NRDC, 2005a). Because there are no standards to which these mold counts can be compared, there is no clear regulatory responsibility among federal agencies for indoor air. High mold counts are cause for concern, however, and both NRDC and EPA recommend that returning residents use respiratory protection and remove all porous construction materials, including carpets and drywall, from flooded homes. The pervasive mold contamination of New Orleans in the aftermath of Hurricane Katrina and the lack of knowledge about the risks of mold and airborne mold spores suggests that additional research is needed to respond effectively to this problem.
The flooding in New Orleans resulted in the potential for unparalleled exposure to toxics and contaminants. Initial concerns about a “toxic gumbo,” however, have not been supported by sampling and analyses to date. Although floodwaters did contain significant short-term biological hazards that posed risks to stranded residents and relief workers, they did not contain chemical toxicants at levels that are expected to lead to long-term impacts on the surroundings beyond the impacts expected of a similar volume of stormwater from the city. The floodwaters undoubtedly redistributed some contaminants, but the contaminant burden in soils and sediments appears to have generated few concerns for acute exposure and risk. However, although acute generalized hazards have not been identified, the population of New Orleans faces localized areas of more serious contamination, such as the neighborhoods impacted by failure of a crude-oil storage tank in St. Bernard Parish.
The most serious short-term issue facing most residents is the presence of high concentrations of mold and airborne mold spores. However, respiratory protection during the removal of all mold-contaminated materials and reconstruction can mitigate the risk.
The results of long-term chronic exposure to contaminants are uncertain, and chemical contamination that exceeds screening guidelines for chronic exposure has been found in some areas. Apparently elevated levels of contaminants can be found in nearly all samples for some constituents, such as arsenic, or, less frequently, PAHs or other hydrocarbons. Exceedences of screening values do not in themselves confirm significant future risk, however, and neither the public nor the local government is likely to accept further delays in rebuilding the city.
There is little scientific basis
for evaluating the health
effects of mold.
The frequency and distribution of exceedances may not differ from pre-Katrina conditions in the city. Thus the question arises as to whether individuals might be willing to delay their return, and even support decisions about which neighborhoods might be rebuilt, based on pre-Katrina contamination levels. The cleanup might be an opportunity to reduce exposure to toxics and other contaminants, regardless of whether the contamination was pre- or post-Katrina. This would undoubtedly require, however, that the citizens of New Orleans accept a diversion of reconstruction funds to environmental cleanup. Other questions involving contamination concerns will influence decisions about which neighborhoods might be changed to lower exposure parklands or other uses, the appropriate balance of expenditures for environmental restoration and flood protection, administrative or legal mechanisms for government to make decisions and for citizens to appeal them, and the role of government condemnations in these decisions.
Unfortunately, currently available data do not show a serious enough contamination problem to encourage government and the public to answer these questions. In the absence of a clear driver for action, decisions about rebuilding are being based on more clearly defined risks, such as the potential for reflooding, and they are being made largely by individuals and third parties, such as insurers, banks, mortgage companies, and, eventually, the courts (in condemnation proceedings). At the same time, governmental entities are trying to build public consensus for governmental proposals.
The critical test of a legal
process is whether the public
perceives it as fair.
Principles for Further Assessments and Rebuilding Decisions
Louisiana RECAP standards call for further assessments and evaluations of areas with contaminants in concentrations that exceed adopted screening standards. Normally (i.e., with no massive catastrophic event, such as Hurricane Katrina), existing institutions (local government, insurers, banks, etc.) could handle the volume of site-specific assessments. However, in the wake of Hurricane Katrina (and, by analogy, other large-scale disasters), decisions must be made based on uniform standards and equity.
First, the scale of decision making in this case and the number of people impacted by decisions about reconstruction are unprecedented. Thus, “off-the-shelf” models cannot be applied.
Second, rules by which decisions are made should be uniform, transparent, and consistent with existing hazardous waste and natural disaster cleanup criteria. History suggests that implementation will be easier if a consensus is reached (at least among governmental entities). Although the destruction in New Orleans is on a very large scale, tools that have been developed and used in the past to make habitability decisions (e.g., Love Canal, Times Beach, World Trade Center, and previous hurricane recoveries) can be adapted.
Third, there must be a balance between the cost of maximizing equity by making case-by-case determinations and the need for making many decisions in a relatively short period of time. In the absence of rapid decisions and answers to the many outstanding questions, individuals will proceed to define the future of New Orleans based on their own circumstances and desires. In that event, uniformity and equity are likely to suffer. In one scenario, individuals or local governments might use reconstruction funds to conduct property owner-by-property owner assessments and use the conclusions to determine remedial action or reconstruction planning. In another scenario, representative sampling might be used by government to make community decisions, and individual property owners might obtain independent samples only to demonstrate the inappropriateness of a community decision as applied to their property.
Finally, there must be a system of checks and balances to ensure that government does not simply “take” individual properties.1 Checks and balances should be based on existing methodologies, such as scientific peer review, public involvement, cooperative efforts between local, state, and federal agencies, and public-private partnerships. The critical test of a legal process is not whether an agency chooses the alternative preferred by the public, but whether the public perceives that the process is fair.
Lessons of Katrina
Ultimately, the lessons learned (or missed) from Katrina should be crystallized in a generic form so that the country as a whole will be better prepared for the next natural disaster, major industrial accident, or act of terrorism. Thus, every effort should be made to put aside partisan concerns to solve real, significant problems in the way information is processed in emergency situations and to make sensible, safe, and equitable cleanup/habitability decisions in an environment of great uncertainty. Because existing institutions were largely unprepared for a disaster of the scale of Katrina, it may not be possible to implement these principles in New Orleans. However, we can learn from Katrina and provide more effective responses to future catastrophes.
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1 The U.S. Constitution Takings Clause states: “Nor shall private property be taken for public use without just compensation.” Thus, there may be legal proceedings at some point about “takings” of property and “just compensation.” Many of the technical issues in such a proceeding are likely to be affected by the policies adopted by the government and private sector to determine the risk associated with each property.