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This report focuses on toxicological assessment of the abandoned waste site. Industrial progress brings obvious benefits to the society, however, it also involves some serious drawbacks, which negatively impact the environment. The site, chosen for toxicological assessment, appears to have numerous drums, containing chemical wastes. In the past six decades, this territory was used by two industrial companies, which no longer exist. Big amount of abandoned waste is the only remainder from the past. Approximate number equals 100. As a result of long term down time, signs of depreciation, such as rust and cracks can be seen on the drums. Absence of labels on the containers makes it impossible to identify substances. In addition, abandoned wastes emit strong smell of pungent chemicals. These facts indicate multiple leaks of possibly toxic substances into the ambience. In accordance with the archived reports from presently defunct companies, the following wastes can be found on the site: acrylamide, chromium waste, PCBs and TDI. Entire situation is complicated by geographical location of the site. There is a popular fishing stream, running through the site. Residential area is situated only one mile upstream, there is also withdrawal point for the local water supply. Downstream water is used for irrigation purposes. The combination of the above-mentioned issues and circumstances comprises the necessity for toxicological assessment. One of the purposes of such evaluation is to thoroughly analyze chemical substances; dwelling on this information will result in the most efficient and productive way of eliminating negative effects on environment.
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It is important to bear in mind that chemicals vary in potency of their toxicity, thus affect surrounding environment in different ways. Hence different methods of destruction should be chosen for ecological clean-up. For instance lipophilic chemicals like PCBs have biologically-accumulative properties; it means that aquatic organisms get contaminated in the result of exposure. As an example, fish captured from the fishing stream, running through abandoned site, contains 520 ppm of PCBs. The use of these pollutants is now restricted; unfortunately, they will remain in water and soil for a long time without the proper treatment. From the previously recorded data four contaminating substances are found on the site. In the pursuit of sufficient assessment, each type of chemical waste should be scrutinized individually.
PCB is poly-chlorinated biphenyls; this toxic pollutant occurs in the result of progressive chlorination of biphenyl, using chlorine gas. This substance is odorless and tasteless semifluid, of clear to pale-yellow color. In accordance with physical properties of PCBs, their water solubility is rather low. On the other hand PCBs have high solubility qualities in organic solvents, as well as high flash point and thermal conductivity. The most common routes of exposure for PCBs include: dermal, oral, inhalation. Specialists argue about recommended exposure limits of this contaminant, however, average mark states 8-10 hours. As for the target organs, which are likely to get affected by this chemical, they are skin, liver and immune system. Potency of PCBs should be also taken into consideration: cancer-inducing, strong resistance to oxidation, reduction, and electrophilic substitution. Mechanism of toxicity involves affecting aryl hydrocarbon receptor (AhR). Owing to the fact, that AhR is a transcription factor, such impact results in cell functioning disruption and gene-transcription mutation. Sometimes estradiol receptor is affected it results in alternation of peculiar DNA segments transcription. Methods of PCBs destruction can be divided according to their nature: physical, microbial and chemical.
Chromium waste was discovered among other contaminants at the abandoned site. This chemical is widely used for industrial purposes. Significant amount of chromium wastes comes from industrial and residential sources. There is a line of chromium forms, based on different oxidation states, the main three of them are: 0, III, VI. Depending on the conditions chromium is placed in, it can shift from one form to another. Scientists have proven the need of chromium III for humans health. There are three main routes of exposure: oral, dermal and inhalation. When it comes to determining exposure limits for chromium, particular issues should be considered first. General norm for chromium III is 20-45 mg\day. When ingested, chromium always shifts into form III for this reason other forms have different type of exposure and therefore exposure limit 500mg\m3, 10 hours. Target organs of this pollutant include: respiratory tract, stomach and small intestine, male reproductive system. Oxidation state of chromium defines its solubility and toxic potency. Chromium VI is considered to be predominant, meaning that it is more potent than chromium III. Mechanism of action of chromium can be described through 1) pharmacokinetic and 2) toxicity mechanisms.
1) Solubility, oxidation state and size of particles as much, as alveolar macrophages activity, are the main factors, defining scale of chromium compounds absorption. It is generally weakly absorbed by gastro-intestinal tract. Jejunum appears to be the main organ for chromium absorption. Eventually absorbed chemical is distributed to all tissues via blood circulation; its biggest concentrations can be found in liver, lung, spleen, kidney, and heart. Depending on the type of exposure and oxidation state, excretion of chromium can last 4-10 hours from inhalation; oral exposure to form III takes 10 hours, while form VI goes up to 40 hours. Dermal exposure does not involve absorption because chromium can be eliminated by washing. Urinal excretion is the main elimination method for chromium.
2) Chromium emits free radicals into blood, which leads to DNA damage on structural and functional levels. Structural lesion results in DNA strand breaks, DNA-protein crosslinks, DNA inter-strand crosslinks, chromosome aberrations. Functional damage comprises: DNA and\or RNA polymerase arrest, mutagenesis, altered gene expression.
It is possible to recover industrial chromium wastes in order to avoid contaminative emissions into the ambience. There are several steps to follow: form VI should be reduced to form III first, then chemical turns into hydrous oxide. Afterwards it is ready for land disposal.
Acrylamide is a multisite cancer-inducing and neurotoxic pollutant. Its properties indicate high solubility and biodegradability in water. For this reason emission of substantial quantities of this pollutant in water can result in oxygen depletion. Acrylamide can be also solved in ethanol, ether and chloroform. Acrylamide is a solid, odorless substance of white color. Different types of acids, bases and oxidizing agents trigger acrylamide decomposition. Non-thermal decomposition produces ammonia, while thermal results in carbon monoxide, carbon dioxide and nitrogen oxide production. Accumulation of the monomer in water is highly unlikely. The most common route of acrylamide exposure is cumulative, peculiar to industrial workers, who experience exposure from day to day. Some other routes include dermal, oral and inhalation exposures. Standard exposure limits for this toxicant are 8-10 hours, 0.70 mg\kg\day. Some researches indicate 548 mg of acrylamide accumulation as a result of 50 years exposure to the chemical. Studies of negative influence of acrylamide on humans show that it generally affects nervous system and reproductive organs. It also induces cancer. Evaluation of acrylamides potency is narrowed down to discovering tumor induction in rats and occasional pancreatic cancer in humans. Action of this contaminant can be described through toxicity mechanism. When ingested, metabolizing process results in production of chemically active epoxide and glycinamide. Studies of acrylamide are limited by bioassays on rodents only. For this reason all data, retrieved from the experiments, has only suggestive status. When implemented to rats, clastogenic effects appear. In addition to that other effects include: chromosome aberrations, micronuclei formation, lethal effects, spindle and cell transformation. Experiments provided sufficient data to support tumor initiating properties of acrylamide. In general it does not create serious hazard for aquatic habitat, with the exception of sites of inappropriate disposal. Preventing contamination can be accomplished through following rules of proper storage, transportation and disposal. Occupational exposure can be avoided by following safety measures. Polymerization into gel is an efficient way of neutralizing toxic properties of acrylamide.
TDI Toluene Diisocyanate is a naturally-occurring compound, consisting of 6 isomers. Similarly to PCBs, this substance is of clear to pale yellow color with low water solubility. TDI is a strong irritating agent, especially to respiratory tract and mucous eye membranes. Some other target organs include pancreas, liver, skin and immune system. Cancer-inducing properties of this contaminant were discovered after multiple bioassays on rats. Cumulative, dermal, oral and inhalation are the most common routes of exposure. Dermal contact may result in marked inflammatory reaction, while respiratory tract irritation can develop into severe chemical bronchitis. In compliance with researches, exposure limits for this toxicant comprise 0.005 ppm (0.04 mg/m3). Considering tumor-inducing potency on rats, TDI presumably has carcinogenic potential for humans. Toxicity activity description demonstrates its mechanism of action. Diisocyanates are known for low eco-to hydrolysis process, this pollutant reacts with other chemicals at room temperature, which results in polymers formation. On one hand, relatively fast hydrolysis of TDI on water surface results in reduced bioaccumulation in the ambience. On the other hand conditions of low humidity prolong lifespan of diisocyanates, which enables them to travel some distance and preserve their toxic properties. Hydrolysis products of TDI present potential hazard when released into air because of their irritating properties. In order to avoid environmental pollution, TDI waste must be properly decontaminated and disposed. There are several methods of destruction; one of them involves adding 4% - 8% ammonium hydroxide, 1% - 2% liquid detergent, 20% nonionic surfactant and 80% water. After chemical reaction TDI forms polyureas. Process of any pollutant disposal must be conducted in compliance with existing law.
Risk assessment is necessary to conduct before any measures of ecological clean-up are taken. Risk evaluation stands for deriving approximate frequency of negative effects, occurring from exposure to a contaminant considering ascertained level of exposure. The calculation should be made using a mathematical model for risk assessment. Depending on the type of toxicant and measuring its influence on the environment risk, management decisions should be made. The best case scenario suggests eliminating contaminant completely. Unfortunately, this option is not always possible, yet there are other opportunities: lowering the level of exposure or shortening its duration. The following steps provide descriptions of steps to be taken in terms of efficient risk assessment: 1) the very first thing to be done is to identify hazard, imposed by a particular substance. 2) This can be accomplished through thorough examination of all pertinent toxicological data. 3) After the estimation of exact number of chemical waste, dose-response assessment should be conducted in order to explore potential health risks from exposure. 4) Researching extent of human exposure is vital. It is usually done through exposure assessment. Calculation of the population, exposed to pollutants, as well as forming ratio between exposed and unexposed population. Afterwards, risk characterization follows.
Based on the 4 steps, described above, toxicological situation of abandoned site can be properly analyzed. The chemical wastes, present on the site impose hazard for water, soil and air contamination. Some of the pollutants can be biologically accumulated in aquatic organisms. Toxicological data shows that PCBs and Chromium waste have low water solubility; this fact enables them to travel long distances and affect surroundings. Acrylamide and TDI on the contrary have high water solubility, but present higher level of inhalation exposure hazard. The range of damage is limited within three miles. The measured number of chemical waste, found on the site goes in the following proportion: 36% PCBs, 22% Chromium, 24% Acrylamide, 18% TDI. Statistic data was used in order to derive ratio of potentially exposed to unexposed population. 5000 people comprise the registered population within 3 miles range. 8% (400) from this population go fishing in the nearest stream; water withdrawal point provides water for 50% of the registered population (2500), 18% (900) individuals use contaminated water for irrigation purposes. Based on the available data, the ratio equals76% to 100% where 76% (3800) have exposure potential. In terms of retrieving some additional information calculation of acceptable daily intake (ADI) can be used. There are several steps to follow: take samples from chemicals, conduct laboratory tests to define exact state and level of toxicological potency, calculate accurate ADI individually for every contaminant. Deriving maximum dose level, which induces no sign of toxicity is of vital importance as well. It is called No-Observed-Adverse-Effect Level (NOAEL). The safety factor must be considered here. NOAEL rarely has 100% accuracy because of possible uncertainty, which occurs during animal tests.
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Based on the waste assessment, the situation on site presents serious toxicological hazard, which should not be ignored. The following activities are recommended for ecological clean-up and exposure prevention:
1. restriction implementation on site access and water usage up and down stream
2. fishing ban in the stream
3. extracting adequate data on the toxicological potency of every contaminant for proper isolation of drums and neutralizing toxic properties of chemicals
4. disposal of each contaminant in compliance with legislation in effect
Realization of all activities, listed above will facilitate environmental improvement on the site and significantly reduce exposure risks for people.
In conclusion, chemical wastes are present due to active industrial manufacturing. Usage of toxic materials and their further disposal are strictly regulated by law and international agreements. There is a strong tendency for shifting industry into environmentally friendly production this fact points to probability of maximal waste reduction in the future. At this point, adverse effects from toxicological exposure can be minimized by following safety rules during handling, transportation and disposal of hazardous substances.