Detection, Treatment And Remediation For Organochlorines

. Organochlorine pollutants are a class of compounds formed by combining chlorine atoms with carbon atoms, and common organochlorine pollutants include chloroform and hexachlorocyclohexane. These compounds are persistent and difficult to degrade, so they exist in the environment for a long time. Organochlorine pollutants pose serious hazards to both humans and the environment. As a result, reducing the release of organochlorine pollutants and strengthening monitoring are important measures to protect the environment and human health. Treatment methods for organochlorine pollutants include physical methods such as adsorption and membrane separation, chemical methods such as oxidation, reduction and hydrolysis, and biological treatment methods such as microbial degradation and biosorption. Treatment of organochlorine pollution has great benefits. Treatment of organochlorine pollution can reduce the harm caused by these pollutants to the environment, improve the quality of water and air, and reduce the hazards of human health. This paper will first discuss what organochlorines are, the types of organochlorines, and the hazards of organochlorines, then discuss how to detect organochlorine residues in water, soil, and air, and finally propose specific methods for dealing with organochlorines and remediation programs for organochlorine pollution in water and soil


Introduction
Organochlorines are organic compounds containing chlorine atoms, usually carbon-chlorine compounds.Organochlorine compounds are a class of compounds that are widely available in nature and synthetically, including many important industrial chemicals and pesticides, among others [1].Organochlorine compounds have a structure in which one or more hydrogen atoms are replaced by chlorine atoms, and this substitution can occur either on the aromatic ring or on the aliphatic hydrocarbon chain.Due to the large electronegativity of the chlorine atom, organochlorine compounds are usually highly stable and inert, as well as toxic and environmentally hazardous.Therefore, the production, use and disposal of organochlorine compounds need to be strictly controlled and managed to protect human health and environmental safety [2].
Organochlorine pollution is the presence of organic compounds containing chlorine atoms in the environment above background levels in the natural environment, causing potential or actual harm to the environment and ecosystems.Organochlorine pollutants are usually caused by human activities, such as industrial production, pesticide use, and waste disposal.These organochlorine compounds are highly stable and inert, difficult to be decomposed and degraded by nature, and therefore persist in the environment, posing a potential threat to ecosystems and human health.The qualities of organochlorines determine their hazards.They can survive in the environment for a long time and can accumulate in the food chain and act on organisms with high nutrient levels.They can migrate over long distances to the distant North Pole.At certain environmental concentrations, they can cause harm or toxicity to organisms that are exposed to the substance.In contrast, in living organisms, the bioconcentration of organochlorines increases with the concentration of organic matter in the food chain.For example, organochlorines in the soil are taken up by plants and multiply their damage once consumed by humans [3].
One more important reason for banning the use of organochlorine pesticides is that they are particularly harmful to the human body.Organochlorines can accumulate in tissues such as the heart and liver, and because of the high fat solubility of this pesticide, they accumulate most in fat.A substance that affects the regulation and regulation of the human body by influencing the processes of synthesis, release, operation, metabolism and binding of normal secretions in the human body.Particularly in cancer, which is currently receiving the most attention, organochlorines have the effect of stimulating and promoting a wide range of tumors.Take breast cancer as an example, Bernhard Schwartlander pointed out that after seventeen years of follow-up and analysis, organochlorine compounds have estrogenic effects, and exposure to organochlorine compounds will increase the likelihood of developing breast cancer.The amount of organochlorine pesticide residues in the breast tissues of patients with breast cancer was significantly higher than that in the control group.In the breast tissue of breast cancer patients, organochlorine pesticide residues were significantly higher than those in the control group.Another example is gallbladder cancer, which has a very high mortality rate.Although there is no significant difference in the blood levels of pesticides in either gallstone disease or gallbladder cancer, BHC and DDT were found in high concentrations in bile, which is very likely to indicate that organochlorine pesticides may be related to gallbladder cancer.And, many other common cancers in life like rectal cancer, brain cancer, prostate cancer [4], all can be affected by organochlorine substances to increase morbidity [5].
Although organochlorine pollutants in the environment have been greatly reduced and eventually disappeared, due to the semi-volatile nature of organochlorine pollutants, places already contaminated with organochlorines will be deposited elsewhere through the "global distillation effect" and the "manganese bomb jumping effect", and even remote areas of the earth have been detected with organochlorines in the polar regions.Organochlorine has been detected even in the remote areas of the earth, and the poor self-healing ability of the polar regions makes it more difficult to degrade organochlorine, which has caused immeasurable damage to the environment.Therefore, we need to find suitable ways to reduce organochlorine pollution and protect the environment.

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Characteristics and types of organochlorine pollution

Characteristics
There are two main aspects.Most of the organochlorines are low cost and relatively simple to manufacture due to the easy availability of raw materials.And they are chemically stable and do not degrade easily.Why said chlorinated and for the great harm, most of the organochlorine compounds in the water solubility is small in the fat solubility is very high not easy to decompose easy to cause environmental residues and cause pollution it is highly efficient, highly toxic and high residual pesticides are very easy to accumulate in the environment.It has been reported that it takes about 20 years to decompose 95% of hexachlorobenzene (HCB) in soil, and 30 years to decompose 95% of DDT.Meanwhile, it can also accumulate in animals through bioconcentration and food chain transmission, bringing great potential danger to human health [6].

Polychlorinated biphenyls (PCBs)
PCBs were first synthesized by H. Schmitt and G. Schulz in Germany in 1881.Polyvinyl chloride (PVC) type organochlorine pesticides, which are man-made organic compounds with persistence, were first synthesized in the United States in 1929.It is estimated that well over 1 million tons of PCBs have been produced and are in application worldwide, of which 1/4 to 1/3 have entered the human environment and caused harm.PCBs are chemically stable and do not decompose rapidly by hydrolysis or similar reactions.Nature's decomposition relies on microbial enzymes in the soil and on ultraviolet light from sunlight, but is not very efficient.As a result, PCBs remain in the environment for a considerable period of time and are hazardous to the atmospheric and aqueous environments [7].

Di-p-chlorophenyltrichloroethane (DDT)
DDT was first invented in 1874 by Ottmar Chindler, but its effect on insecticides was only discovered in 1939 by Miller of Switzerland.DDT is a white crystal insoluble in water and is an effective insecticide.For the first half of the 20th century to control agricultural pests and diseases, reduce malaria typhoid fever and other mosquito and fly-borne disease hazards played a considerable role.However, it has been banned in many countries and regions because it pollutes the environment too much.DDT has a strong effect of carcinogenicity, teratogenicity, and mutagenicity, and the main manifestations of chronic toxicity are: loss of appetite, pain in the epigastric region and the right ribs, headache, dizziness, muscle weakness, fatigue, insomnia, visual and speech disorders, tremor, anemia, and decreased deep reflexes of the limbs.There are liver and kidney damage, skin lesions, cardiac arrhythmia, weak heart sound, sinus bradycardia, bundle branch conduction block and rdial damage.DDT under certain conditions undergoes a series of biological and environmental degradation, among which DDE is produced by removing hydrogen chloride.DDE has very little toxicity to insects and high-level animals, and is not easy to be degraded by the living creatures and the environment, so DDE is the main residual substance [8].

Detection of organochlorines in soil
Soil is the main carrier for the implementation of organochlorine pesticides, and it is an important part of the ecosystem.Organochlorine pesticide residues in soil are volatilized and diffused in various ways, which ultimately affects human health, so the detection of organochlorine compounds in soil is a very important issue.Soil detection is a kind of trace detection, which needs to be carried out by using highly sensitive and modernized instruments, and at present, HPLC, gas chromatography, TLC, TLC and so on are mainly used in China.And soil organochlorine detection methods include electron capture detector-gas chromatography and gas chromatography-mass spectrometry, which is a mass spectrometry-chromatography coupling method and can be used in our daily learning life.The most effective method is the solid phase extraction/gas chromatography-mass spectrometry (SPE/GC-MS) method, which allows the simultaneous determination of 23 organochlorine pesticides (OCPs) in soil and the study of compensation methods for different matrix effects.Pre-treatment is necessary because OCPs are characterized by low water solubility and strong hydrophobicity making them susceptible to adsorption on suspended particulate matter and eventually accumulate in sediment and soil.Pre-treatment is divided into extraction and purification, and because of the large number of analyses to be carried out, fast, efficient and automated pre-treatments such as pre-treatment and solid-phase extraction were chosen, and the main methods of analysis were GC and tandem mass spectrometry.Using the above methods, the organochlorine content in soil can be determined under specific conditions, and the results obtained can be used to calculate the matrix effect.Soil contamination is an important problem in the detection of pesticide residues, which is related to the type of pesticide, the type of sample, and the principle of the detection instrument.The polarity and heat resistance of pesticides play a decisive role in the matrix effect, and the effect of the same pesticide in different specimens has some differences.On this basis, a new detection technology is known as biosensing, which is a new technology capable of generating a selective and reversible response to a particular pesticide or insecticide by tightly combining a biologically active substance with an energy converter.Currently used for most pesticide residue analysis and detection of biosensors, is the use of pH-altering technology, the principle of pH determination can be based on the inhibition of enzyme detection [9].

Detection of organochlorine in water
Water is also involved in many aspects of agricultural production and life, whether soil leakage into the water or other reasons, the detection of chlorine compounds in the water also appears to be very important, so check the information to understand a very effective methodliquid-liquid extraction a gas chromatography triple quadrupole mass spectrometry multi-reaction.Although the commonly used analytical method is gas chromatography-electron capture detector method, however, organochlorine samples are often very complex, easy to be interfered with and reduce sensitivity.Triple quadrupole mass spectrometry (TQMS) is a rapid analytical technique that has been applied to organochlorines and PCBs in soil, and it is characterized by very good resistance to interference and high sensitivity, which overcomes the shortcomings of water samples that are difficult to characterize and have low sensitivity.In multiple reaction monitoring (MRM), primary mass spectrometry selects ions with specific mass-to-charge ratios, generates fragment ions in a triple quadrupole collision cell, and then characterizes and quantifies them by selecting specific fragment ions through secondary mass spectrometry.The second stage mass spectrometry removes most of the chemical background, and in general, the charge ratio of interfering substances is almost zero, so it has low qualitative, quantitative and detection limits, which makes it a highly desirable method, especially in complex water quality samples [10].

Detection of organochlorines in the atmosphere
The above two are routine for the detection of organochlorine, respectively, proposed in the water and soil detection methods, with the development of urban industry, atmospheric pollution has become one of the most serious problems faced by mankind, the increase in the concentration of atmospheric pollutants, not only can cause respiratory diseases, heart disease and skin diseases, but also cause a variety of cancers, and even death, so the degree of harm of atmospheric pollution can be said to be the most important of all the environmental pollution.Therefore, the degree of harm of air pollution can be said to be the first of all environmental pollution.The main means of monitoring organochlorine in the atmosphere is biomonitoring.Biological monitoring is the use of biological reflection of pollutants in the atmosphere, the composition and content of polluted gases to monitor.At the same time, plants can effectively exchange with the atmosphere through a large number of leaves; they lack an animal circulatory system that can mitigate the effects of the external environment; and their stationary growth characteristics prevent them from avoiding pollution.Because of their sensitivity to the air, combined with their fixed geographic location and ease of monitoring and management, plants are the primary means of atmospheric pollution.Chlorine, on the other hand, can enter the roots and leaves of plants through various pathways, but its main pathway is the leaves, where chlorine ions accumulate due to their hydrophilic nature and eventually enter the body of the plant.Chlorine has a strong killing effect on chloroplasts and can rapidly destroy chlorophyll, causing the leaves to lose green, fade and decolorize, and in severe cases, the entire leaf will turn white and fall off.The toxicity of chlorine gas to plants is 3~5 times that of sulfur dioxide.After the plant suffers damage, its growth and results will be greatly affected.By refining and analyzing it by sulfonation method and column chromatography, the detection of chlorine organics can be realized [11].

Treatment of organochlorines 4.1 Significance of organochlorine treatment
Organochlorine compounds are potentially harmful to the environment and ecosystems because they are highly stable and inert, and difficult to degrade and decompose in the natural environment.The significance of treating organochlorine pollutants is to protect the environment and human health, and to reduce the impact of organochlorines on ecosystems.Through effective treatment methods, it is possible to reduce the concentration of organochlorine compounds in the environment and minimize their contamination of water, soil and air, thus maintaining ecological balance and sustainable development.

Biodegradation
Polychlorinated biphenyls (PCBs) were first synthesized by H. Schmitt and G. Schulz in Germany in 1881.Polyvinyl chloride (PVC) type organochlorine pesticides, which are man-made organic compounds with persistence, were first synthesized in the United States in 1929.The degradation process of organochlorine compounds can be accelerated by screening and cultivating adaptable microbial strains.Biodegradation methods have the advantages of being environmentally friendly and economically efficient, but suitable environmental conditions and selection of microbial strains need to be considered.
Enzymes are not only indispensable to living systems, they are also outstanding catalysts.Enzymes, like any catalyst, are not consumed in a chemical reaction and can only increase the reaction rate of a chemical reaction without changing the equilibrium constant of the reaction.What makes enzymes unique as catalysts is their higher specificity compared to most other catalysts.Bioremediation has become the optimal choice due to its environmental friendliness and low economic cost, especially for the anaerobic degradation of PCBs involving reductive dechlorination, and the preferred degradation is perchlorinated PCBs.Currently the anaerobic strains of PCB-degrading bacteria have been widely studied, including Desulfomoniletiedjei, dehaloccoidesmccartyi, desulfitobacterium, dehalospirillummultivorans, and dehaloccoidesethenogenes, dehalococcoidesmccartyi, desulfitobacterium, dehalospirillummultivorans and dehalococcoidesethenogenes.As the research continues, it has been shown that the addition of compounds such as glucose, acetone and methanol can act as electron donors in the dechlorination reduction reaction, thereby increasing the ability of microorganisms to metabolize PCBs.
As shown in Fig. 1, the biological treatment and the reality of the actual combination of there is a method, called A2/O-MBR combined process, organic chlorine and then the process is mainly subjected to sludge adsorption, biodegradation and sludge adsorption [12].

Adsorption
Adsorption of organochlorine compounds by adsorbents is used to remove them from water or wastewater.The adsorbent can be activated carbon, zeolite, polymers, and the adsorption method has the advantages of low cost, simple equipment, and stable results, and has become an effective method for treating both high and low concentrations of pollutants in water or oil.
Crude oil contains trichloromethane, carbon tetrachloride, 1,2-dichloroethane, tetrachloroethylene, 1,2-dichlorobenzene and other organic chlorides.When they enter the subsequent processing equipment with the oil, they will not only generate HCl, which will seriously corrode the reaction equipment and valves and pipe fittings, causing great safety hazards, but also cause poisoning of the hydrogenation refining catalyst and catalytic reforming catalyst.Under high temperature conditions, activated carbon shows good effect of chemical adsorption and dechlorination, and oxidative modification can increase the acidic functional groups on the surface of activated carbon to improve its adsorption and dechlorination capacity, however, due to the fact that the loss of activated carbon in the process of regeneration is often relatively large, and the adsorption capacity after regeneration decreases, which restricts its industrial application, so molecular sieve dechlorination adsorbent is introduced.The molecular sieve dechlorination adsorbent has a wide range of applications.At room temperature, the molecular sieve shows a good physical adsorption effect on organic chlorine, and the adsorption and dechlorination performance can be further improved by metal ion loading or ion exchange modification of the molecular sieve.Not only that, at higher temperatures (>100 ℃ ), molecular sieves can also chemisorb organochlorine, and the stronger the surface B acid, the stronger the chemisorption effect.In addition, the molecular sieve can be regenerated by air thermal oxidation, and the cycle of regeneration performance is good, it is a very promising dechlorination adsorbent for industrialization [13], as shown in Fig. 2. In addition, there have been innovations in the adsorption of organochlorines in water bodies, the main one being the introduction of iodine species to effectively increase the enrichment capacity of hierarchical porous silica oxides for specific organochlorines, such as hexachlorohexane.The efficiency of adsorption of hexachlorohexane by SiO2-I obtained with different amounts of I-silane is given in the figure below.It is certain that this new composite material based on the halogen bond adsorption mechanism provides a new efficient and convenient way for the enrichment and separation of organochlorine pollutants in water, which has a great application prospect in the fields of sample pre-treatment and pollutant removal [14].

Chemical treatment
Chemical treatment of organochlorine mainly includes oxidation, reduction and hydrolysis.Oxidation is the process of converting organochlorine compounds into inorganic chlorides or other harmless substances, commonly used oxidizing agents are ozone, hydrogen peroxide and so on.Reduction is through the reducing agent will organochlorine compounds to inorganic chloride or other harmless substances, commonly used reducing agents are sulphite and iron powder.Hydrolysis is the decomposition of organochlorine compounds into inorganic chlorides and other compounds through the action of water molecules, commonly used hydrolysis methods include alkaline hydrolysis and acid hydrolysis.These chemical treatment methods can effectively degrade organochlorine pollutants and reduce their impact on the environment.
Organochlorine pollutants are oxidized to harmless substances such as inorganic salts or carbon dioxide by means of oxidizing agents such as hydrogen peroxide and potassium permanganate.This method is suitable for water and wastewater treatment.
An oxidation method, advanced oxidation, is highlighted.One oxidation system, the iron-activated sulfite system, was previously studied.Advanced oxidation techniques (AOPs) are new and efficient technologies for the removal of organic pollutants with high chemical stability and low biodegradability.Compared with hydroxyl radicals, sulfate radicals have higher redox potentials (2.5-3.1 V) In some cases, sulfate radicals have higher selectivity and longer half-life than hydroxyl radicals for selective and efficient degradation of organic matter.In recent years sulfate radicals have been extensively studied for the removal of organic pollutants such as pharmaceuticals and personal care products (PPCPs), endocrine disruptors (EDCs), and other difficult to degrade organic compounds.Sulfite (S(IV)) can be activated by transition metal ions to form thioredoxin radicals via a chain reaction, including sulfite radicals (SO3-•), peroxysulfate radicals (SO5-•), and highly oxidizing SO4-•, which in turn can react to form highly oxidizing SO4-•.-and can react to generate highly oxidizing OH-, these radicals can quickly and efficiently oxidize and remove most of the organic pollutants in the water, and also have a very good effect in the treatment of difficult to degrade organic matter.Organochlorine pollutants are reduced to inorganic or low-toxicity organic substances by means of reducing agents such as sulfites and iron powder.This method is suitable for soil and wastewater treatment.
The more cutting-edge methods include the monoatomic iron method.At the beginning of its reduction reaction, the reducing agent (such as sulfite) will be adsorbed onto the surface of monoatomic iron, and the electrons in the reducing agent will be transferred from the reducing agent molecules to the metal ions on the surface of the monoatomic iron, so that it can be reduced to metal atoms; at the same time as the transfer of electrons, the cations in the reducing agent molecules will react with the anions on the surface of the monoatomic iron, in order to maintain the charge equilibrium, and in the process, the organochlorine can be reduced by the electron gain or loss on its surface to render organochlorine harmless; after the process of electron transfer and charge balance, metal ions are gradually reduced to metal atoms and generated on the surface of monatomic iron [15].
Hydrogenation of organochlorine pollutants to form harmless alkanes or alcohols using hydrogen as a reducing agent.This method is suitable for the treatment of organic synthetic waste.
The mechanism is that chlorinated organic pollutants are added to an alkaline solution to obtain an electrolytic reaction solution, and the electrolytic reaction is carried out in a diaphragm-less electrolyser with a palladiummodified conductive material as the cathode and a chemically-affective conductive material as the anode to obtain a completely dechlorinated compound, thus achieving the effect of treating organochlorines [16].

Remediation of organochlorine pollution in soil
It is the remediation of organochlorine in soil, soil as the main negative carrier of pesticides in the process of crop production and planting, due to the low water solubility and strong fat solubility of OCPs destroyed the structure of the soil and the microbial environment, the OCPs residue in the soil, the continuous accumulation and the various pathways to pass, always affecting the food safety and human health.The remediation techniques are categorized into physical and chemical remediation.Physical remediation includes soil vapor leaching remediation, thermal desorption remediation, electrokinetic remediation and so on.The first two technologies are more traditional, while electrokinetic remediation is a new type of green in situ remediation technology that is not limited by soil heterogeneity and low permeability.It is characterized by the removal of pollutants through power supply to the contaminated land, and the removal of organic pollutants through electrodynamic and electrochemical methods by electroseepage into the electrode area.It is characterized by faster remediation, lower costs and the use of fewer chemicals.Whereas chemical methods include traditional methods such as soil drenching and redox, there is also an emerging method called photocatalytic degradation.It is a kind of chemical reaction using photocatalysts and photocatalysts to generate free radicals with high activity and use their substitution, addition and electron transfer to decompose organic pollutants into harmless or innocuous organic substances.The method employs advanced oxidation technologies, such as the well-known Fenton system, which is an advanced oxidation system.However, the biological activity of the soil is reduced due to factors such as soil organic matter content, pH, soil thickness, soil particle size, and water content.Many experiments have demonstrated that a rapid reaction through free radicals can lead to a rapid equilibrium and rapid removal of organochlorine pollution.

Remediation of organochlorine pollution in water bodies
The remediation of organochlorine wastewater can still be divided into physical and chemical methods.Physical method used more is the extraction method and adsorption method, the use of two different physical properties and the extraction of organochlorine pollutants to achieve the effect of purification.In addition, the gas extraction method and membrane treatment method also see the corresponding report, but in practice is rarely used.However, purely physical methods cannot be completely removed, but only through migration, if the operation is not appropriate, it is likely to produce secondary pollution of the environment, so it is difficult to promote in the project, and the feasibility is also very low.Therefore, physical methods are usually used for pre-treatment or posttreatment, or more than two physical methods for pollution control, but usually not a single method, so the chemical method is used.The Fenton method is a commonly used chemical method, which attacks the organic matter by the hydroxyl group generated by the Fenton reagent, thus realizing the degradation of the organic matter.In addition to the photocatalytic degradation mentioned above, newer methods include ultrasonic radiation oxidation.Its basic principle is: when the ultrasonic wave exceeds 15 kHz, the tiny bubbles in the polluted wastewater will be excited and produce the ultrasonic cavitation phenomenon, and the cavitated bubbles will form a region of high temperature and high-pressure area in a very small range, and under the extremely high temperature and pressure, the water vapor in the vacuole decomposes into extremely strong oxidizing radicals, which oxidize with the pollutants and realize biodegradation.In the practical application of organochlorine pesticide pollution site is often accompanied by organochlorine pesticides, pesticide intermediates, organic solvents, heavy metals, antibiotics, microplastics and even nanomaterials of the composite pollution, so dealing with organochlorine pesticide composite pollution of the microbial degradation technology is the future direction of a development.

Conclusion
Organochlorine compounds are a class of organic compounds containing chlorine atoms, which are widely found in industrial production and agricultural applications, and cause serious harm to the environment and ecosystems: they are highly toxic, causing direct damage to aquatic organisms and terrestrial ecosystems, and have strong persistence and bioconcentration, which can persist in the environment for a long period of time and gradually accumulate, with destructive effects on the ecological balance; and most importantly, some OCs have been proved to be carcinogenic and teratogenic, posing potential threats to human health.Most importantly, some organochlorine compounds have been shown to be carcinogenic and teratogenic, posing a potential threat to human health.Currently, the problem of organochlorine pollution is becoming more and more serious globally.Many industrial effluents and pesticide residues contain large amounts of organochlorine compounds, leading to contamination of water bodies and soil.In addition, organochlorine pollutants in the atmosphere are increasing, negatively affecting air quality.This state of affairs forces us to adopt effective treatment means to reduce organochlorine pollution.
Fortunately, people are now beginning to recognize the seriousness of the problem and have launched a series of means to solve the problem of organochlorine pollution.Common methods include physical treatment, such as adsorption, membrane separation and oxidation.Adsorption technology removes organochlorine contaminants from water or air through adsorbents.Membrane separation technology utilizes a semipermeable membrane to separate organochlorine contaminants from water or air.Oxidation technology converts organochlorine contaminants into harmless substances by means of oxidizing agents.In addition, biodegradation is also an effective means of treatment, utilizing microorganisms to degrade organochlorine pollutants and convert them into harmless substances.Of course, the most direct and thorough treatment is the chemical method.
In the future, we should strengthen the monitoring and control of organochlorine pollution.By establishing stricter laws, regulations and standards, and strengthening the regulation of industrial wastewater and pesticide use, we can reduce the emission and use of organochlorine pollutants.At the same time, scientific research should be intensified to develop more efficient and low-cost treatment technologies for organochlorine pollutants.