Dioxin contamination, Times beach, Missouri, USA.
Letort Vanessa
Student Number: 2029474
Module Number: HEV 3211
Purchase Diane
PORTFOLIO ASSIGNMENT
CASE STUDY: DIOXIN CONTAMINATION, TIMES BEACH, MISSOURI, USA.
Dioxin is a general term that describes a group of hundreds of chemicals that are highly persistent in the environment. Dioxins and furans are some of the most toxic chemicals known to science (Porteous, 2000).
The most toxic compound is 2,3,7,8-tetrachlorodibenzo-p-dioxin or TCDD. The toxicity of other dioxins and chemicals like PCBs that act like dioxin are measured in relation to TCDD. Dioxin was the primary toxic component of Agent Orange.
Dioxin is formed as an unintentional by-product of many industrial processes involving chlorine such as waste incineration, chemical and pesticide manufacturing and pulp and paper bleaching. Dioxin is formed by burning chlorine-based chemical compounds with hydrocarbons.
The major source of dioxin in the environment comes from waste-burning incinerators of various sorts and also from backyard burn-barrels. Dioxin pollution is also affiliated with the production of Polyvinyl Chloride (PVC) plastics (Internet 1).
Dioxins are a serious public health threat. According to a draft report released for public comment in September 1994 by the US Environmental Protection Agency (EPAS, there is no safe level of exposure to dioxin. After publication of a research paper from the International Agency for Research on Cancer (IARC) (1997), 2,3,7,8-TCDD was considered as a Class 1 carcinogen. In 2003 re-analysis of the cancer risk from dioxin reaffirmed that there is no known "safe dose" or "threshold" below which dioxin will not cause cancer (Internet 2).
In addition to cancer, exposure to dioxin can also cause severe reproductive and developmental problems (at levels 100 times lower than those associated with its cancer causing effects). Dioxin is known for its ability to damage the immune system and interfere with hormonal systems.
The major sources of dioxin are in diet. Since dioxin is fat-soluble, it bioaccumulates, climbing up the food chain and it is mainly (97.5%) found in meat and dairy products (beef, dairy products, milk, chicken, pork, fish and eggs). In fish alone, these toxins bioaccumulate up the food chain so that dioxin levels in fish are 100,000 times that of the surrounding environment.
Below is a diagram displaying food sources of dioxin (Figure 1):
Figure 1: Background TEQ exposures for North America by pathway
Chart from EPA Dioxin Reassessment Summary 4/94 - Vol. 1, p. 37
(A TEQ is a dioxin Toxic EQuivalent, calculated by looking at all toxic dioxins and furans and measuring them in terms of the most toxic form of dioxin, 2,3,7,8-TCDD).
In late December 1982, the inhabitants of the little town of Times Beach, Missouri, received news that they had to evacuate their homes, as the whole state was considered contaminated by dioxin.
The contamination was caused by the negligence of NEPACCO, a chemical and pharmaceutical company, who had failed to properly dispose of their waste products. The company primarily produced a bactericide, hexachlorophene. Hexachlorophene was made from trichlorophenol, which is known to contain dioxin. Agent Orange is also made from trichlorophenol, and the company was associated with a producer of Agent Orange.
Dioxin removed from hexachlorophene production went into dioxin-containing water, clay, and still bottom; a thick, smelly residue that contained highly concentrated dioxin from the processes.
At first, those wastes were sent to Louisiana for incineration. However, the cost of this procedure was high and the management then decided to subcontract the Independent Petrochemical Corporation to dispose of the waste. Another independent subcontractor, Russell Bliss was then in charge of disposing of the waste. The still bottoms waste were then either buried on the company site an the rest sold to farmer to spread on the ground for dust settling and hoof root prevention in cattles. The contaminated water was send to the nearby Water and Wastewater Technical School in Neosho. In 1980, the head of the school examined the content of the water and sent a sample for testing. The dioxin level was 2 ppm, about the amount in Agent Orange used during Vietnam. The next year, the EPA removed the water, the tank, and surrounding soil for secure burial (Internet 3).
It seems that NEPACCO failed to inform the subcontractors of the nature of the waste. Record shown that Bliss sprayed Times Beach's 23 miles of dirt road periodically between 1972 and 1976. He had also dumped oil in the town. To make matter worst, Times Beach was regularly subject to heavy flooding, and one of the worst flooding took place December 5th 1982.
Upon discovering the contamination, EPA had to permanently relocate more than 2,000 people and demolish all of the homes and businesses. The level of dioxin was tested between 1 ppm and 127 ppm. Now, a new State Park is replacing what was one of the most highly contaminated sites in the US.
This major contamination in the state of Missouri resulted in the total evacuation of the town and the estimated cost of $35 million, not to mention the impact upon the inhabitants health, who are still monitored today (EPA, 1983).
The contamination, however, did not only occur at Times Beach, but 33 other sites were then declared contaminated in the state of Missouri.
After evacuation, EPA had to start working on a way to remediate the contamination. A feasibility study, including a risk assessment, was undertaken to determine the extent of the contamination and exposure and what type of remediation would be applied to dioxin-contaminated soils.
In September 1988, a Record of Decision (ROD) (EPA, 1988) was signed and specified that on-site incineration would be the remediation technology for the excavated soil and debris of the Times Beach area. This decision was made after careful consideration for other remediation technologies available at the time. The feasibility study considered seven remedial alternatives, including a no-action alternative, which was later dismissed because "it would not adequately protect public health and the environment" (EPA, 1984). Following (Table 1) are the six other remedial alternatives proposed by the EPA feasibility studies, together with their estimated cost:
Alternatives
Cost
Stabilize soil in place
$41.5 M
Interim storage on-site
$35 M
Disposal off-site
$32.2 M
Incineration
$111.6 M
Solvent extraction
$151.6 M
Interim storage off-site
$15.7 M
Table 1: Alternatives remedial technologies and cost proposed by EPA feasibility study (1984)
The incineration and solvent extraction technologies have the advantages of reducing dioxin levels and reducing the need for long term monitoring and surveillance. EPA opted for the incineration technology, as they believed that this remedy provided a permanent solution to the dioxin contamination problem in eastern Missouri. The main disadvantage of this procedure was the implication of greater soil handling than containment option, increasing the risks of contamination for workers.
The cost of cleanup for Times Beach and Minker/Stout/Romaine Creek (other contaminated sites) was estimated at $50 million. Total cost to incinerate the soil from the other sites in eastern Missouri was estimated to be $120 million (EPA, 1984).
The risk assessment study from EPA considered the overall risk to residents, workers and environment, exposure risk to residents (especially children) and workers, potential for erosion and dusting, maintenance of neighbourhoods and property values, and long term effects on Missouri and its citizens.
A public audit was undertaken in 1984. The extent of the contamination was ...
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The cost of cleanup for Times Beach and Minker/Stout/Romaine Creek (other contaminated sites) was estimated at $50 million. Total cost to incinerate the soil from the other sites in eastern Missouri was estimated to be $120 million (EPA, 1984).
The risk assessment study from EPA considered the overall risk to residents, workers and environment, exposure risk to residents (especially children) and workers, potential for erosion and dusting, maintenance of neighbourhoods and property values, and long term effects on Missouri and its citizens.
A public audit was undertaken in 1984. The extent of the contamination was investigated by EPA by systematically sampling the soil in the areas at risk, considering the vertical movement of surface water and the potential contamination of shallow aquifer, and the migration of the contaminant. The main worry was that the Times Beach area is located on a flood plain, and heavy rain might disperse the contaminant. Previous action was taken at Times Beach to construct a series of spur levees surrounding the site to prevent floodwater from carrying contaminated soil off site (EPA, 1984).
About 265,000 tons of contaminated soil and debris from Times Beach and 28 other sites in eastern Missouri were incinerated from March 1996 to June 1997 in an incinerator built and operated on the site by Syntex, the parent company of NEPACCO. The cleanup cost the government a total of $110 million, $10 million of which was reimbursed by Syntex. After the cleanup, the incinerator was dismantled and the site was turned over to the State of Missouri (WSTB, 2003).
However, many problems arose after and during the remediation process due to a lack of efficiency, knowledge, and relevance of the risk assessment undertaken by EPA.
Indeed, it is expected that combustion by-products from the incineration of one particular chemical would lead to emission of closely related chemicals as combustion by-products. This has been the case for incineration of hazardous waste in general (Harrisson, 1996). For example, incineration of polychlorinated biphenyls (PCBs) leads to the emission of polychlorinated dibenzo-furans, a very closely related chemical in terms of structure and composition. PCB fires leads to creation of both furans and polychlorinated biphenylenes, another closely related chemical. The incineration of dioxin also leads to formation of dioxin as a combustion by-product. (Harrisson, 1996). However, an article in Riverfront Times in November 1996 (Stelzer, 1996a), revealed that "the risk assessment for the Times Beach incinerator did not consider PCBs or their priority pollutants that were in the soil to be burned (a clear violation of federal law) and that many EPA sampling records from many of the 27 sites were missing from the agency's files".
The same author also revealed that EPA and Missouri DNR have refused to consider abundant evidence indicating that some of the PCBs in eastern Missouri came from another source. This source of dioxin and PCBs was from Monsanto plants. In February 9, 1983, Russell Bliss himself testified before a hearing of the Missouri Hazardous Waste Management Commission
that he had a contract with Monsanto to haul away chemical wastes. Moreover, based on evidences presented at trial, a judge in Cole County, Missouri, November 30, 1984, concluded that Russell Bliss had dumped hazardous wastes, including PCBs, in Dittmer, Missouri and that "the only known source" of one of the chemicals (bromophenyl chlorophenyl ether) was Monsanto (Environmental Research Foundation, 1997a).
Bioavaibility is also a parameter that has not be taken into account during the risk assessment leading to the choice of remediation technique used at Times Beach. The inclusion of site-specific bioavailability information has been judged important in a number of cases, and uncertainties were addressed at a level appropriate to risk-based decision making (WSTB, 2003). The case of Times Beach is considered a "prominent example" where "site-specific assessments of bioavailability processes were not used to guide remediation decision-making" (WSTB, 2003). Ignoring bioavailibilty of a contaminant can lead to poor decisions making regarding exposure assessment, which has implications for how much contamination should be cleaned up and at what cost. A contaminated site could be excavated even if the contaminants are not bioavailable. This could increase the bioavailability of the material and potentially the risk to other receptors, such as wildlife, that were not originally the receptors of concern.
The EPA's chosen methods of risk assessment and standards of unacceptable risk has also been critically studied by Harrisson in 1996.In his study, he denounced the fact that the EPA do not include multi-pathway risk assessments in their work, meaning that some routes of exposure are not taken into account such as the mother's milk route for dioxin.
The technique of remediation did not prove to be a total success and EPA's own internal documents admitted that the incinerator could not destroy dioxin with the efficiency required by law (99.9999% destruction and removal efficiency) (Environmental Research Foundation, 1997b).
In addition, a few incidental release of dioxin happened during the incineration process. In 1996, two emergency releases of dioxin-laden pollutants at the Times Beach incinerator occurred (Stelzer, 1996b). According to the EPA's initial Times Beach risk assessment, a typical emergency venting could occur at a frequency of once per week and last for several minutes. Because of the absence of a gas cleaning system, approximately 350 pounds of treated particulate matter may be emitted during a typical release. Those occurrences are referred to as an Environmentally Safe Temporary Emergency Release (ESTER). In a subsequent risk assessment, the EPA called ESTER events "hypothetical." (Internet 4).
The Times Beach Action Group (TBAG) described the all operation "dishonest".
TBAG showed that "chain of custody" had been broken for samples taken from the incinerator. (Chain of custody is a strict, legal paper trail that shows who took what samples when, to assure that samples have not been falsified or tampered with). They also revealed the laboratory analysing the samples for the Times Beach incinerator was half owned by the incinerator company, which presented a clear conflict of interest (Stelzer, 1996c).
Finally, the group revealed that EPA and the federal Centres for Disease Control (CDC) knew about the contamination throughout eastern Missouri in 1974 but waited nine years before taking any action to protect the public. Stelzer caught EPA officials in "outright lies" (Seltzer, 1996d) when they claimed they knew nothing about dioxin contamination in Missouri until "after 1980."
The evacuation itself was also questionned. Subsequent research on the effects of dioxin on humans and other mammals has led some experts to question whether the evacuation of the town was necessary, sometimes citing the example of Seveso, Italy, the site of a disaster in1976 that exposed residents to larger levels of dioxin than those of Times Beach and whose subsequent cleanup allowed the city to continue to exist (Internet 5).
The incineration process did not seem to be the most efficient and might have been more efficient if conjugate with a solidification and stabilization (S&S) technique. Indeed, some S&S techniques have proved effective for stabilizing residue resulting form chemical or thermal treatment of dioxin contaminated material (OTA, 1991).
In the case of Times Beach, Missouri, clean-up work could have been delayed until alternative technologies were proven efficient for dioxin remediation. Aboveground, elevated storage buildings are large, permanent buildings constructed of pre- stressed concrete in which dioxin-contaminated materials might be stored temporarily in drums or containers.
Indeed, in 1996, thermal techniques such as incineration for dioxin remediation in soil seemed to be the most appropriate technique available. However, as stated in the background paper on dioxin treatment technologies (OTA, 1991) from the U.S. Congress, Office of Technology, there was a limited knowledge on incineration technique at the time, implying costly research project to be undertaken before clean up could occur at Times Beach.
Today, it is possible to use ionising radiation to destroy pollutants adsorbed to soils. It has been shown that gamma radiation emitted by the radioactive decay of Cobalt-60 will reductively dechlorinate dioxins on soils (Zacheis, et al., 2000). Unlike other methods of soil remediation, radiolysis offers the possibility of soil treatment without phase separation. In the case of thermal desorption and incineration, contaminant volatilisation from the soil surface may lead to the emission of toxic compounds. Another advantage of radiolysis is that it may be economically competitive to methods such as incineration (Gray and Clelland, 1998).
The long-term human effect of dioxin is still not fully understood. It might eventually turn out that they are not as concerning as scientists think. However, it is always better to be cautious of something that is dangerous. A dumpster full of debris is all that remains of the last building left standing in Times Beach, Missouri. Residents were not notified about the contamination until ten years after the incident, the evacuation and clean up were poorly handled, and there have been years of legal battles seeking just compensation. This dramatic event raises significant questions about the close ties between government officials and the chemical industry in minimizing the dangers of dioxin. "The environmental disaster in Times Beach is an important cautionary tale with wide relevance, especially for the thousands of communities potentially at risk from toxic pollution." stated a journalist from the Eco Outlet (Internet 6).
REFERENCES
> Environmental Research Foundation. 1997a. Rachel's Environment & Health Weekly #563.
> Environmental Research Foundation. 1997b. Rachel's Environment & Health Weekly #280, #312.
> EPA press release- February 22, 1983. Joint Federal/State Action Taken to Relocate Times Beach Residents.
> EPA press release - September 30, 1988. Times beach Record of Decision Signed.
> EPA Feasibility Study. 1984. EPA/ROD/RO7-84/002.
> Gray, K. A. Clelland, M. R. 1998. Environmental radiolysis for soil and sediment treatment: A review of chemistry, design, and economic issues. Adv. Ox. Technol., 3, 22-36.
> Harrisson, M. 1996. GreenLaw Preliminary Risk Analysis of the Army Chemical Weapon Incineration Program. Kentuky Environmental foundation.
> IARC. 1997. Monographs on the Evaluation of Carcinogenic Risks to Humans and their Supplements: Volume 69 Polychlorinated Dibenzo-para-Dioxins and Polychlorinated Dibenzofurans. ISBN 92 832 1269 X.
> OTA Dioxin Treatment Technologies: 1991. U.S. Office of Technology Assessment (OTA); Washington, D.C.; OTA-BP-O-93.
> Stelzer, C. D. 1996a. Why the Times Beach Incinerator Should be Shut Down. Riverfront Times. November 20, 1996.
Available on the world wide web at: http://home.stlnet.com/cdstelzer/index.html.
> Stelzer, C. D. 1996b. Riverfront Times (St Louis), April 3, 1996.
Available on the world wide web at: http://home.stlnet.com/cdstelzer/index.html
> Stelzer, C. D. 1996c. Twice Burned. Riverfront Times. August 28, 1996.
Available on the world wide web at: http://home.stlnet.com/cdstelzer/index.html.
> Stelzer, C. D. 1996d. Dangerous Ground --Dioxins aren't the only problem in Missouri. PCB contamination continues to be overlooked or denied by both public regulators and Monsanto. Riverfront Times. February 14, 1996, pg. 1.
Available on the world wide web at: http://home.stlnet.com/cdstelzer/index.html.
> (WSTB) Water Science and Technology Board. 2003. Bioavailability of Contaminants in Soils and Sediments: Processes, Tools, and Applications.
> Zacheis, G. A. Gray, K. A. and Kamat, P. V. 2000. Radiolytic degradation of hexachlorobenzene on three field soils: A comparison of electron beam and gamma
radiation. Environ. Sci. Technol.
> Internet 1: Dioxin
http://www.ejnet.org/dioxin/
> Internet 2: No Evidence of Dioxin Cancer Threshold
http://www.ejnet.org/dioxin/nosafedose.html
> Internet 3: Death of a town
http://syngen2.chem.brandeis.edu/~walker/timesbch.html
> Internet 4: Times Beach Dispatches
http://lists.essential.org/1996/dioxin-l/msg00247.html
> Internet 5: Times Beach, Missouri.
http://en.wikipedia.org/wiki/Times_Beach,_Missouri
> Internet 6: Eco Outlet
http://shop.ecoiq.com/acb/showdetl.cfm?&DID=23&Product_ID=1740&CATID=155
SHORT QUESTIONS
. Definitions
a) Orphan sites:
Orphan sites are sites contaminated by a release of hazardous substances, where the release presents a serious human health and environmental problem, and where the people responsible for the hazardous substance contamination are unknown, or are unwilling or unable to pay for a cleanup.
b) Kow :
Kow is the octanol-water partition coefficient. It is the ratio of the concentration of a chemical in octanol and in water at equilibrium and at specified temperature. Octanol is an organic solvent that is used as a surrogate for natural organic matter. This parameter is used in many environmental studies to help determine the fate of chemicals in the environment. The octanol-water partition coefficient has been correlated to water solubility. The physical meaning of Kow is the tendency of a chemical to partition itself between an organic phase (e.g., PAHs in a solvent) and an aqueous phase. Chemicals that have a low Kow value (<10) may be considered relatively hydrophilic; they tend to have a high water solubility, small oil/sediment adsorption coefficients, and small bioconcentration factors for aquatic life. Conversely, a chemical with a large Kow (>104) is considered hydrophobic and tends to accumulate at organic surfaces, such as on humic soil and aquatic species.
c) Desk study:
This is a term used in contamination investigation. The desk study is the preliminary investigation, used to assess whether the site is contaminated and presents a potential risk. Different sources of information are considered, documentary evidence and site reconnaissance.
d) LD50:
In toxicology, the LD50 of a particular substance is a measure of how much constitutes a lethal dose. It is expressed in units of mass of substance per mass of body mass. It is tested by administration of varying doses of a substance to populations of test animals; the dose administered which kills half the test population is referred to as the LD50.
e) NOAEL:
NOAEL stands for no-observed-adverse-effect-level. It is the greatest concentration of a substance, found by experiment or observation, which causes no detectable adverse alteration of morphology, functional capacity, growth, development, or life span of the target organism under defined conditions of exposure.
f) Eh:
Eh is the oxidation-reduction potential of the material being considered when oxidation-reduction types of chemical reactions are involved. Maintaining a low Eh in the liquid phase enhances anaerobic biologic decomposition of certain halogenated organic compounds.
g) ICRCL action level:
The ICRCL (The Interdepartmental Committee on the Redevelopment of Contaminated Land) publication introduced the concept of Trigger concentrations (Threshold and Action) to assist in determining the extent to which a site is contaminated. Assigned Trigger concentrations vary depending on the proposed end use of the land. For domestic developments where risks exist of direct ingestion of soil or consumption of contaminated food grown on the site, the acceptable levels are lower than for commercial or industrial development where these risks are less.
2. Methods of treatment for soil contamination
Treatment method
VOC
ABS
HAL
PAH
PCB
Soil washing
Electrokinetic method
Air sparging
Pump and treat
Thermal desorption method
Natural attenuation
Phytoremediation
Biopile
3. Calculation of fraction of pollutant in soil
CT = ? CS+ ?CW+ ?gCG,
where ? is the bulk soil density, and ? and ?g are respectively the volumetric water and air content in soil. And Henry's Law CG = H x CW
And Freundlich isotherm CS = K x CW
Thus, CG = 0.5 x 14.5 = 7.25 mg/ml
CS = 5 x 14.5 = 72.5 mg/ml
CT = 0.08 x 72.5 + 0.2 x 14.5 + 0.05 x 7.25 = 9.0625 mg/ml
And XW = CW/CT x 100 = 14.5/9.0625 x 100 = 2.48%
XS = CS/CT x 100 = 72.5/583.2625 x 100 = 12.43%
XG = CG/CT x 100 = 7.25/583.2625 x 100 = 1.24%
4. Biological indicator
a) Simpson's index and Jaccard's index
Simpson's index: D = 1- ? ??? ???????????????? : proportion of the total sample
composed of the ith species.
SPECIES
SUSPECTED SITE 1
pi 1
CONTROL SITE 2
Pi 2
Ji
A
40
0.04
0
0.0066
B
300
0.3
00
0.066
C
00
0.1
55
0.0366
D
0
0
5
0.0033
E
50
0.15
300
0.2
F
60
0.16
400
0.266
G
0
0
22
0.0813
H
0
0
8
0.0053
I
50
0.05
0
0
J
5
0.005
0
0
K
0
0
00
0.066
L
20
0.02
50
0.1
M
0
0
20
0.0133
N
0
0
80
0.0533
O
15
0.115
0
0
P
7
0.007
50
0.033
Q
0
0
5
0.0033
R
3
0.003
65
0.0433
S
2
0.012
0
0
T
38
0.038
30
0.02
TOTAL
000
500
a = 13
b = 16
j = 9
????0.1675 D1 = 1-0.1675 = 0.8325
There are 83.25% of chances of choosing twice the same species at random for population 1.
??0.1489 D2 = 1-0.1439 = 0.8561
There are 85.61% of chances of choosing twice the same species at random for population 2.
Jaccard's index: J = j / [(a+b)-j] j: number of taxa common to both sample
a: number of taxa in sample from community a
b: number of taxa in sample from community b
J = 9/ [(13+16)-9] = 0.45 by convention if J is between 0.3 and 0.6, both samples are considered similar.
b) Discussion
The Simpson's index is a diversity index, it is a measure of biodiversity. For both sites, the populations seem to be as diverse as each other (0.8325 and 0.85861). The Jaccard's index compare the similarity of both site's population. According to the Jaccard's index, list of species found in both communities are similar.
Therefore, although the number of individual of each species is different in each sites, calculation indicate that at a community level the pollutant did not affect the species. Indeed, the control population is as diverse as the suspected population and the Jaccard's index indicates a similarity between populations of both sites.
REVIEW QUESTIONS
. QUESTION 1
"The environment is intricately related. Pollution in land may affect the groundwater and atmospheric fallout can constitute a major source of land contaminants".
Although, our natural inclination is to subdivide the biosphere into compartments such as land, ocean, atmosphere, and so on, chemical compounds move from one environmental compartment to another to fulfil the necessary processes of life. Indeed, during photosynthesis, plants will fix atmospheric CO2 to produce carbohydrates. These transfers of chemical compounds occur all the time in natural systems, and so does pollutants transfer. Diffuse sources of pollution such as the dispersion of heavy metals and organic compounds in the atmosphere will subsequently influence soil quality by deposition.
Figure 1 displays a simplified transfer path of a chemical compound between environmental compartments.
Figure 1: Transfer between environmental compartments.
Pollutants release into the environment will move around different environmental compartment unless they are controlled.
When dioxin pollution occurred at Times Beach, Missouri, 1982, the release of this contaminant via the spreading of oil onto the soil, made it available to fish in rivers due to dioxin bioavailibility by leaching and flood events and ultimately in seas.
The importance of studying environmental mobility of chemical compounds is justified by the fact that once dispersed in the environment, chemical compounds will never disappear.
The environmental mobility of a pollutant is its ability to move between environmental compartments. The more mobile a compound is the more possibilities organisms have to be exposed to it.
2. QUESTION 3
Bioindicators of soils.
The term bioindicator is used for organisms or organism associations, which respond to pollutant, load with changes in vital functions, or which accumulate pollutants. The most important reasons for using bioindicators are:
- The direct determination of biological effects,
- the determination of synergetic and antagonistic effects of multiple pollutants on
an organism,
- the early recognition of pollutant damage to plants as well as toxic dangers to
humans
- a relatively low cost compared to technical measuring methods.
Bioindicators are commonly grouped into accumulation indicators and response indicators. Accumulation indicators store pollutants without any evident changes in their metabolisms. Response indicators react with cell changes or visible symptoms of damage when taking up even small amounts of harmful substances.
Biomonitoring is divided into passive and active. Passive biomonitoring is the use of organisms, organism associations, and parts of organisms, which are a natural component of the ecosystem and appear there spontaneously. Active biomonitoring includes all methods, which insert organisms under controlled conditions into the site to be monitored. Figure 2 displays examples of bioindicators that can be used for active and passive monitoring. (Source: Berlin digital Atlas, Internet site http://www.stadtentwicklung.berlin.de/umwelt/umweltatlas/ed307_01.htm).
Figure 2: Examples of bioindicators, active and passive methods.
In application, earthworm can be used to indicate the presence of heavy metal pollution in soils. The application of bioindication techniques may provide information on the availability of contaminants, and may thus help to support management decisions. In addition, the repeated application of bioindicators may reveal temporal trends and the spatial extent of the ecological effects of contaminants. For example, invertebrates are part of the soil life-support system.
3. QUESTION 4
a) Dose-response assessment and ecological based risk assessment
A risk assessment has four components: hazard identification, dose-response assessment, exposure assessment and risk characterization. The dose-response assessment is the second of four steps in risk assessment, consisting of the analysis of the relationship between the total amount of an agent absorbed by a group of organisms and the changes developed in the group in reaction to the agent, and inferences derived from such an analysis with respect to the entire population, i.e. it determines the relationship between the magnitude of human exposure and the probability of human health effects.
The dose-response assessment is primarily aiming to establish the amount that can cause damages and how a change in dose will influence the likelihood or frequency of adverse effects. The traditional deterministic approach has been to establish the no-effect level (NOEL) or lowest-observed-effect level (LOEL), and subsequently divide by an uncertainty factor to obtain the tolerable or acceptable daily intake (TDI/ADI) (Source: Robyn Fairman, Carl D. Mead and W. Peter Williams, King's College, London Environmental Risk Assessment - Approaches, Experiences and Information Sources Environmental issue report No 4).
An ecological based risk assessment is a scientific process for estimating, with a known degree of certainty, anthropogenic effects on the integrity of natural ecosystems and the services they provide. Ecological Risk Assessment (EcoRA) involves the assessment of the risks posed by the presence of substances released to the environment by man, in theory, on all living organisms in the variety of ecosystems, which make up the environment.
EcoRA is a whole study of the impact of an anthropogenic chemical species which is or will be release into the environment, where as dose-response assessment is a necessary study part of a health risk assessment. Health risk assessment is concerned with individuals and morbidity and mortality, EcoRA is concerned with populations and communities and the effects of substances on mortality and fecundity. EcoRA has to deal with a multitude of organisms, all with varying sensitivities to chemicals and various groups have distinct exposure scenarios.
The principal limitation of a dose response assessment is related to the fact that most studies are done on animals. Thus, tolerable intakes have to be derived from data obtained from animal exposure, and must include uncertainty factors to account for variabilities and uncertainties. Those variabilities and uncertainties relate mainly to extrapolation from animal studies to the human situation and to "inter-individual" variability within the response for the human population. Traditionally, default factors of 10 have been applied to account for each of these variations.
Thus, the principal limitation of such assessment is the lack of a fully developed biologically based dose-response models.
The principal limitation to an ecological based risk assessment is related to the extrapolation of scales and space. Indeed, scientific data related to a specific stressor are limited to what can be obtained in a controlled laboratory setting or in a limited field study. In most assessments, the scales of interest in decision-making are substantially larger in space and of longer duration than could be accommodated in any practical assessment effort. Some form of extrapolation, either with explicit mathematical models or with judgment-based decision rules, is necessary to make the risk assessments useful for decision-making.
Thus, both types of assessment need their results to be extrapolated to the actual subject studied.
b) Risk assessment and risk management
It is important to note the difference between Risk Assessment and Risk Management. Risk assessment only evaluates the risk that contamination poses; Risk management evaluates the management options (corrective actions) for sites at risk.
Figure 3: The elements of risk assessment (source: Fairman and Mead)
The traditional goal of regulating risks is to protect and improve public health and well being.
Risk assessment, comprising the elements of hazard identification, dose-response assessment, exposure assessment and risk characterization, is an essential tool used by many national, regional, and international bodies. A risk assessment is an information to decision-makers. Risk characterization aims to provide a synthesis of estimates of exposure levels and health risks; it also summarizes sources of uncertainty in scientific data and provides the primary basis for making risk management decisions. The results of a risk assessment (as summarized in the characterization) are the basis of identification of chemical exposures that pose no significant health threat and those that present significant risks. This helps risk managers evaluate a range of options. It assists risk management officials and decision makers in allocating resources and money to the most important resolvable uncertainties and reduction of risks. Risk management relates to all the activities required to reach decisions on whether an associated risk requires elimination or necessary reduction. Risk management is a complex multidisciplinary procedure.
[References:
Fairman, R. and Mead, C. 1996 Approaches to Risk Assessment. Unpublished.
Proposed Guidelines for Ecological Risk Assessment. U.S. Environmental Protection Agency, Risk Assessment Forum, Washington, DC, 1996.]
