HCH is a synthetic organochlorinated pollutant. There are eight isomeric versions of HCH. α-, β-, γ-, and δ-HCH are the four most universal isomers shown in Figure 1 ^[1]. γ-HCH (also known as lindane) is the most frequent isomer, and it is general. As the global usage of HCH decreases, so does the frequency of detection and the amounts identified in the environment ^[2].

In general, HCH formulation is a mixture of β- (5–12%), δ- (6–10%), γ (10–12%), and α- (60–70%) isomers. However, only the γ-HCH isomer shows the maximum insecticidal activity. Therefore, it is used more in the agriculture sector than the other three isomers. γ-HCH is purified to at least 99% and the other isomers are discarded or not sent to the market ^[3].

HCH isomers are widely dispersed in the environment. They accumulate in the food chain and cause toxicity in biological systems due to their lipophilic characteristics. They are volatilized in the environment and transferred to far-flung locations. As a result, HCH isomers are among nature’s most persistent and commonly encountered pollutants, with polluted sites documented all over the world. The half-life of lindane in soil and water was estimated to be 708 and 2292 days, respectively ^[4]. Lindane and other HCHs leftovers survive in the environment for a long time and have lately been found in water, soil, sediments, plants, and animals all over the world owing to their persistence ^[5].

O.E. Fayemi et al. ^[6] prepared the environmentally friendly modified working electrodes by altering the surface of a glassy carbon electrode (GCE) using polyaniline nanofibers (PANI), nanoparticles (ZnO and Fe₃O₄), and multiwalled carbon nanotubes (MWCNTs). GCE is used as a material for electrodes in electrochemistry, as well as for high-temperature crucibles due to its thermostability, chemical resistance, and impermeability to gases and liquids. Researchers prepared two types of composite electrodes (PANI/Zn, Fe(III) and Nylon 6,6/MWCNT/Zn, Fe(III)). Once preparing the electrodes, the researchers used cyclic voltammetry (CV) to observe the reduction behavior of lindane. Both composite electrodes and bare GCE displayed irreversible (reduction) CV peaks. Both the composite electrodes showed increased reduction peak currents for lindane electron-transfer reactions. GCE modified from Nylon 6,6/MWCNT/Fe₃O showed the maximum sensing current because of improved diffusion of lindane molecules through the micropores of Nylon 6,6/MWCNT/MO nanofibers. They also performed the analysis of lindane in tap-water samples and obtained a recovery range performance.

A. Kumaravel et al. ^[7] prepared stable and reproducible cellulose acetate (CA)-modified GCE to sense lindane in the aqueous-alcoholic medium. The researchers prepared the modified GCE using a drop-dry method (deposited CA solution on pretreated GCE). They have also used CV to test the electrode performance for sensing lindane. The researchers observed the reduction peak of lindane at −1.5 V at both bare GCE and CA-modified GCE. However, at the CA-modified GCE, the reduction peak currents are quite high due to the CA-modified electron-transfer mechanism. They tested the analytical utility of the electrode in drinking water samples. They have used CV, differential pulse voltammetry (DPV), and amperometry to measure lindane in drinking-water samples. The recovery of lindane is higher at DPV.

Anu Prathap et al. ^[8] detected lindane using NiCo₂O₄ modified glassy carbon electrode using differential pulse voltammetry (DPV) and cyclic voltammetry in the aqueous-methanol medium. At −1.5 V of the reduction peak, it shows a single well-defined irreversible lindane reduction. After the modification of the electrode, the reduction of lindane electron transfer can be calculated by the Randles–Sevcik equation. This modified GCE shows that lindane is irreversibly reduced, as there is no longer a reverse peak. They used four different metal oxides as an electrode, but all of these were found inactive to detect the reduction of lindane. Only NiCo2O4-modified GCEs are found to show a higher current response compared to other metal oxide electrodes. Researchers have used CV, DPV, and amperometry techniques for the detection of lindane in tap water with good recovery in differential pulse voltammetry (DPV). The GCE–AONP–PANI–SWCNT modified electrode was used in this experiment, and square wave voltammograms were obtained with varied lindane concentrations. After the modification of GCE with NiCo₂O_4, it showed excellent electrolytic activity enhanced the electron transfer rate, and gave a detection limit of 37,000 nM. It was discovered that when the concentration of lindane increased, the lindane reduction peak current increased as well, and the potential gradually switched to the negative side ^[9]. The linear graph’s standard deviation error value was found to be 0.21. The detection limit (LOD) for lindane at the GCE–AONP–PANI–SWCNT modified electrode was calculated using the relationship 3.3/m, where m is the slope of the same line and r is the relative standard deviation of the intercept of the y-coordinates. The GCE–AONP–PANI–SWCNT electrode’s limit of detection (LOD), the limit of quantification (LOQ), and sensitivity to lindane were determined to be 2.01 nM, 6.09 nM, and 202.5 µA/µM, respectively^[6]. This shows that the AONP–PANI–SWCNT-modified GCE has a superior electrocatalytic activity for lindane electrooxidation. The results showed that the GCE–AONP–PANI–SWCNT-modified electrode demonstrated anti-interference behavior when detecting lindane in the presence of interfering species (benzene, cyclohexane, phenol, Ca²⁺, Fe²⁺, K⁺, and Mg²⁺), with an average current drop of only 12.1 percent on the lindane reduction signal. To determine the practical application of the GCE–AONP–PANI–SWCNT-modified electrode for lindane detection in both river-water and tap-water samples, a real sample analysis was performed. Lindane/water samples with concentrations ranging from 0.5 to 100 M were generated using a 60:40 methanol/river-water mixture containing 0.05 M TBAB, and CV tests were conducted to measure the quantity of lindane in the samples. The recovery value of lindane at lower concentrations was found to be higher than the presence of lindane in river-water samples. The sensor’s kinetic range could be responsible for this result.

Abdul Rahim Mohd Yusoff ^[9] proposed Nylon 6,6 modified graphite HB pencil as a working electrode to detect lindane using differential pulse cathodic stripping voltammetry (DPCSV). Researchers replaced the traditional mercury electrode to avoid the toxicity of mercury with economical HB pencil electrodes with Nylon 6,6 graphite HB pencil electrodes. Pencil graphite electrodes have received a lot of attention because of their low background currents, exceptional sensitivity, repeatability, implementable electroactive surface area, cost-effectiveness, and convenience of discharge. To modify the pencil electrode researchers, use alumina paste, ethanol, and Nylon 6,6 solution. This modified electrode is proved that it has good stability, a good recovery percentage, and a low concentration could be determined. The recovery percentage of pesticides for water sample analysis was calculated using the following Equation.

4. Electrochemical Reduction of Lindane