**12. Conclusions**

**Treatment Matrix Conditions Efficiency Reference**

81% removal COD [30]

[31]

[32]

[33]

[34]

[35]

93% removal endosulfan

83% removal endosulfan

95% removal endosulfan

Complete disappearance of endosulfan

Complete degradation

Water Concentration of endosulfan: 6 g/L

Ozone dosage: 57 mg/min Reaction time: 60 min

dose: 50 mg/mL

dose: 236 mg/mL

Continuous shaking: 130 rpm

Water Concentration of endosulfan: 20 mg/L

Contaminated water: 200 mL

Soil Concentration of endosulfan: 400 mg/ml

Incubation time: samples were taken at 12 h

β-endosulfan 12.03 and 6.87 mg/kg, respectively.

SiO<sup>3</sup>

Photocatalyst: nitrogen-doped anatase TiO<sup>2</sup>

Contact time: 250 min Agitation rate: 200 rpm

interval up to 144 h Temperature: 30 ± 2°C Rotary shaker: 120 rpm

Soil Concentration of endosulfan: α- and

under visible-light irradiation. Eluents: Tween 80, SDS and Na<sup>2</sup>

Reaction time: 240 min Temperature: 25 ± 2°C in dark Rotary shaker: 200 rpm

Reaction time: 1 h

Temperature: 30°C

Adsorbent: 0.2 g

Reaction time: 2 h

pH: 6

Ozonation Water Concentration of endosulfan: 10 mg/L

pH: 10

Fenton Water Concentration of endosulfan: 7.5 mg/L FeSO<sup>4</sup>

> H2 O2

pH: 3

pH: 7

Soil: 5 g

pH: 6.8

Soil: 25 g

pH: 6.23

Supporting electrolyte: NaCl (1 g/L) Current density: 60 mA cm−<sup>2</sup>

Electrooxidation by boron-doped diamond anode

12 Persistent Organic Pollutants

Adsorption with sawdust carbon

Biodegradation by *Aspergillus niger*

Photocatalytic degradation with the elution of surfactants

One of the most important economic activities worldwide is agriculture. Form the early 50s and owing to population growth, intensive agriculture practice has been carried out. In this kind of massive production, an excess of chemical substances was used, among them, pesticides. Endosulfan has been one of the most used pesticides due to its wide spectrum of activity; nevertheless, it has very negative consequences on the environment. The physicochemical properties of endosulfan favor bioaccumulation and biomagnification, and it is considered a persistent organic compound; thereby, in 2007, it was proposed to be included in the Stockholm agreement, aim that was reached in 2010. Thanks to the information gathered, a large number of countries have banned the use of endosulfan; however, many other countries still use it on their fields. It has been found that endosulfan is transported to zones considerably far from the application fields, as an example, endosulfan has been detected in the Arctic. Although a large number of countries have opted not to make use of this pesticide, research continues in order to find out how to eliminate it from soil, sediments, water, and a proper disposal of the product that that will be no longer used [37–39].

## **Author details**

Claudia Rosales Landeros<sup>1</sup> , Carlos Eduardo Barrera Díaz<sup>1</sup> \* and Bryan Bilyeu<sup>2</sup>

\*Address all correspondence to: cbd0044@gmail.com

1 Centro Conjunto de Investigación en Química Sustentable UAEM—UNAM, Toluca, Estado de México, México

2 Department of Chemistry, Xavier University of Louisiana, New Orleans, LA, USA

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**Chapter 3**

**Provisional chapter**

**Degradation Pathways of Persistent Organic Pollutants**

**Degradation Pathways of Persistent Organic Pollutants** 

Persistent organic pollutants (POPs) are resistant to most of the known environmental degradation processes. Because of their persistence, POPs bioaccumulate in animal tissues and biomagnify along food chains and food webs with potential adverse impacts on human and wildlife health and the environment. Although POPs are resistant to most of the environmental degradation processes, there are some environmental processes mostly microbial degradation that can degrade POPs to other forms that are not necessarily simpler and less toxic. The Stockholm Convention on Persistent Organic Pollutants adopted in 2001 was meant to restrict the production and use of these toxic chemicals in

**Keywords:** degradation, POPs, bioaccumulation, biomagnification, Stockholm

Persistent organic pollutants (POPs) are toxic organic compounds that are resistant to most of the degradation processes in the environment, and therefore they tend to persist in the environment, thus bioaccumulating in organisms and biomagnifying along the food chains and food webs in ecosystems. POPs pose a risk of causing adverse effects to human and wildlife health in particular and the environment in general. POPs include a wide class of chemical species with different physicochemical properties and toxicologies. The priority list of POPs consists of pesticides such as dichloro diphenyl trichloroethane (DDT), hexachlorocyclohexanes (HCHs), and hexachlorobenzenes (HCBs), industrial chemicals such as polychlorinated biphenyls (PCBs), and unintentional by-products of industrial processes such as

> © 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use,

distribution, and reproduction in any medium, provided the original work is properly cited.

DOI: 10.5772/intechopen.79645

**(POPs) in the Environment**

**(POPs) in the Environment**

http://dx.doi.org/10.5772/intechopen.79645

Additional information is available at the end of the chapter

Additional information is available at the end of the chapter

James T. Zacharia

**Abstract**

the environment.

convention

**1. Introduction**

James T. Zacharia


#### **Degradation Pathways of Persistent Organic Pollutants (POPs) in the Environment Degradation Pathways of Persistent Organic Pollutants (POPs) in the Environment**

DOI: 10.5772/intechopen.79645

James T. Zacharia James T. Zacharia

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[37] Bhalerao S, Puranik P. Biodegradation of organochlorine pesticide, endosulfan, by a fungal soil isolate, *Aspergillus niger*. International Biodeterioration and Biodegradation.

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[39] Pillai P, Kottekottil J. Nano-phytotechnological remediation of endosulfan using zero valent iron nanoparticles. Journal of Environmental Protection. 2016;**7**(05):734-744

dane using Fenton's reagent. Applied Water Science. 2014;**7**(1):207-215

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2015;**15**(9):1909-1918

Additional information is available at the end of the chapter Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.79645

#### **Abstract**

Persistent organic pollutants (POPs) are resistant to most of the known environmental degradation processes. Because of their persistence, POPs bioaccumulate in animal tissues and biomagnify along food chains and food webs with potential adverse impacts on human and wildlife health and the environment. Although POPs are resistant to most of the environmental degradation processes, there are some environmental processes mostly microbial degradation that can degrade POPs to other forms that are not necessarily simpler and less toxic. The Stockholm Convention on Persistent Organic Pollutants adopted in 2001 was meant to restrict the production and use of these toxic chemicals in the environment.

**Keywords:** degradation, POPs, bioaccumulation, biomagnification, Stockholm convention

### **1. Introduction**

Persistent organic pollutants (POPs) are toxic organic compounds that are resistant to most of the degradation processes in the environment, and therefore they tend to persist in the environment, thus bioaccumulating in organisms and biomagnifying along the food chains and food webs in ecosystems. POPs pose a risk of causing adverse effects to human and wildlife health in particular and the environment in general. POPs include a wide class of chemical species with different physicochemical properties and toxicologies. The priority list of POPs consists of pesticides such as dichloro diphenyl trichloroethane (DDT), hexachlorocyclohexanes (HCHs), and hexachlorobenzenes (HCBs), industrial chemicals such as polychlorinated biphenyls (PCBs), and unintentional by-products of industrial processes such as

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

polychlorinated dibenzo-*p*-dioxins and dibenzofurans (PCDDs/PCDFs) and polycyclic aromatic hydrocarbons (PAHs). The first priority list of POPs consisted of 12 compounds commonly referred as the dirty dozen by the Stockholm Convention that was adopted in 2001.

their use, transportation, storage, and disposal of obsolete pesticides. Some other chemicals [polychlorinated biphenyls (PCBs), pentachlorophenol] are used as oils, as dielectric and cooling fluids in capacitors and transformers, for wood preservation, etc., and are released into the environment as a result of spills and evaporation. A number of substances like dioxins/ furans, polycyclic aromatic hydrocarbons (PAHs), and hexachlorobenzene are by-products of many industrial processes, mainly, thermal (fuel combustion and waste incineration, ferrous industry, coke and aluminum production, road transport, chemical synthesis of chlorinated

Degradation Pathways of Persistent Organic Pollutants (POPs) in the Environment

http://dx.doi.org/10.5772/intechopen.79645

19

**3. Why are POPs resistant to most of the environmental degradation** 

In the initial list of the Stockholm Convention, POPs are typically polyhalogenated organic compounds which exhibit high lipid solubility. For this reason, they bioaccumulate in fatty tissues of animals. Halogenated compounds also exhibit great stability reflecting the nonreactivity of C-Cl bonds toward hydrolysis and photolytic degradation in the environment. The high electronegativity of halogens compared to carbon gives the carbon-halogen bond a significant polarity/dipole moment. The electron density is concentrated around the halogen, leaving the carbon relatively electron poor. This introduces ionic character to the bond through partial

between them, contributing to the unusual bond strength of the carbon-halogen bonds. The carbon-halogen bonds are known to be "the strongest in organic chemistry," because halogen forms the strongest single bond to carbon [3, 4]. The bond also strengthens and shortens as

The stability and lipophilicity of persistent organic compounds often correlate with their halogen content; thus, polyhalogenated organic compounds are of particular concern. They exert their negative effects on the environment through two processes, long-range transport, which allows them to travel far from their source, and bioaccumulation, which reconcentrates

POP exposure may cause developmental defects, chronic illnesses, and death. Some are carcinogens, possibly including breast cancer. Many POPs are capable of endocrine disruption within the reproductive system, the central nervous system, or the immune system. People and animals are exposed to POPs mostly through their diet, occupationally, or while growing in the womb [6]. For humans not exposed to POPs through accidental or occupational means, over 90% of exposure comes from animal food products due to bioaccumulation in fat tissues and bioaccumulation through the food chain. In general, POP serum levels increase with age

more halogens are added to the same carbon on a chemical compound.

these chemical compounds to potentially dangerous levels in animal tissues [5].

Clδ−). The partial charges on the chlorine and carbon exert electrostatic attraction

substances, etc.) and are emitted directly into the air (**Figure 1**) [2].

**processes?**

charges (Cδ<sup>+</sup>

**4. Health effects of POPs**

and tend to be higher in females than males [7].

Over the last decade, the priority list of POPs has been updated to include such compounds like brominated flame retardants (BFRs), such as polybrominated diphenyl ethers (PBDEs), listed under the Stockholm Convention in 2017 [1], and hexabromocyclododecanes (HBCDDs), currently under consideration for listing. A further group of recently recognized halogenated POPs are the perfluorinated alkyl substances, of which perfluorooctane sulfonate (PFOS), its salts, and perfluorooctane sulfonyl fluoride were also added to the Stockholm list in 2017. Other compounds in the new list include endosulfan, lindane, pentachlorobenzene, chlordecone, and hexabromocyclododecane (HBCD).

POPs have a tendency to persist in the environment for long periods, are capable of longrange transport, bioaccumulate in human and animal tissue and biomagnify in food chains and food webs, and have potential significant adverse impacts on human health and the environment. Exposure to POPs can cause serious health problems including certain cancers, birth defects, dysfunctional immune and reproductive systems, greater susceptibility to disease, and even diminished intelligence. Of all known POPs so far, the organochlorine compounds, including polychlorinated dibenzo-*p*-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs), and polychlorinated biphenyls (PCBs), have received the most attention due to their persistence in the environment, bioaccumulation, biomagnification, and hazard effects to biota.
