# Recent Strategies for Environmental Remediation of Organochlorine Pesticides
## 3 Methods for Removal of Organochlorine Pesticides from the Environment
One zero-valence iron transfers two electrons to oxygen, which then reduces the oxygen to hydrogen peroxide, while the zero-valence iron is oxidized to iron(II). Another zero-valence iron donates two electrons to the hydrogen peroxide generated from the first reaction to form water. The last step involves the reaction between iron (II) and hydrogen peroxide to generate the hydroxyl radicals. Figure 3.1 Photo–Fenton degradation of organochlorine pesticides. Adapted with permission from [63]. Copyright (2012) American Chemical Society. The generated highly oxidizing hydroxyl radical degrades the pesticides to nontoxic or less-toxic substances [64]. Equations (8)-(10) present the reactions that occur in the process:  
Figure 3.2  
Figure 3.3  
Figure 3.4  
[PERSON] et al. [42] used zero-valence iron and iron oxide to destroy organochlorine pesticides (aldrin, lindane and DDT) from water. The products obtained were investigated and the degradation pathway for p,p-DDT was proposed (Figure 5). However, the intermediate products of lindane and aldrin were not identified. It was noted that within 12 h, about 79.81% and 100% of aldrin, HCH and DDT were successfully degraded, respectively. [PERSON] et al. [43] also redchlorinated soils that has been contaminated with organochlorine pesticides. This was carried out by using iron at oxidation state of zero at an abandoned production site. Other reported methods that have been used for the treatment of organochlorine compounds include thermal desorption, air stripping, settling, membrane filtration, hydrolysis, vitrification, solar destruction, reverse osmosis and solvent extraction [25]. Each of these methods have their advantages and shortcomings. For example, solvent extraction cannot destroy the organochlorine pesticides, but transfers it from one medium to another, which requires another complementary remediation method with solvent extraction. Sometimes, more than one method may be combined to get a better removal  
Figure 3.5 Degradation pathway of p,p-dichlordiphenyltrichloroethane (DDT) using zero-valence iron. Reprinted from [42]. Copyright (2016), with permission from Elsevier. efficiency of organochlorine pesticides. Example was the degradation of DDT using both plasma and thermal desorption strategies, reported by [PERSON] et al. [65]. The continuous search for new strategies for the remediation of the environment from organochlorine pesticides led to the emergence of heterogeneous catalysis as one of the preferred environmental remediation techniques. It is preferred to other methods that had been discussed because it utilizes solar light which is abundantly available. In addition, it can degrade pesticides at ambient pressure and temperature instead of transferring them from one medium to another which could lead to secondary pollution problem. It is one of the advanced oxidation processes which requires the use of suitable photocatalyst. As shown in Figure 6, an ideal photocatalyst should be chemically and biologically inert, stable to photo corrosion, utilizable in the visible or near UV light region, cheap, nontoxic and photoactive [66]. Example of semiconductors that have been utilized as photocatalysts are metal oxides, metal sulfides, noble metals, graphene oxide, graphitic carbon nitride or their composites.