**4. Physicochemical properties**

ornamental flowers to attack pests [2–4]. It typically enters the atmosphere through agricultural application and can be transported long distances in the air. The levels in the air vary substantially depending on the location. Rural areas tend to have higher levels. Endosulfan half-life in soils is estimated to range from 60 to 800 d, while its half-life in groundwater and

In this chapter, a complete physicochemical description of endosulfan is presented. The degradation sub-products, toxicity, and environmental impacts are described. Finally, some

Endosulfan is an organochlorine insecticide (6,7,8,9,10,10-hexachloro-1,5,5a, 6,9,9a-hexahydro-6, -9-methane-2,3,4-benzo-dioxathiepin-3-oxide) with a CAS Number 115-29-7 that has a cyclodiene structure. It contains a sulfite diester group that is relatively reactive and infers

This pesticide has been widely used since its introduction in the 1954 by Farbwerke Hoechst because it has a broad spectrum of activity. The commercial grade of endosulfan is a mixture of α- and β-endosulfan isomers (**Figure 1**), in a 7:3 ratio, respectively. Its main degradation product is endosulfan sulfate, which has similar properties to the compounds of origin [9–11].

Some of the trade names that have been given to endosulfan are Cyclodan, Thiodan, and Thiosulfan, among others that can be found elsewhere [12]. The trade formulations of endosulfan are emulsifiable, microencapsulated, powder, wettable powder, granules, technical powder, technical solid, and technical liquid, with a concentration for agricultural use of 350–500 d of active ingredient (AI)/L or kg and for industrial use the concentration is 940–970

H6 Cl6 O3 S.

technologies that have been recently applied to treat the residues are described.

persistence in the environment. The condensed chemical formula is C<sup>9</sup>

sediments may increase up to 6 years [5–8].

**3. Trade names, formulations, and use**

**Figure 1.** Structure of isomers α and β endosulfan.

**2. Chemical aspects**

6 Persistent Organic Pollutants

(AI)/L or kg [13].

**Table 1** shows some physicochemical properties of α-endosulfan, β-endosulfan, and endosulfan sulfate [14, 15].

Some of the environmental fates of the endosulfan are related to its physicochemical properties. For instance, the aqueous solubility of the α-isomer is higher than the β-isomer and endosulfan sulfate. Compounds whose solubility is less than 25 mg L−<sup>1</sup> tend to be immobilized in soils and living organisms. The three molecules have partition coefficients octanolwater > 1. Therefore, they are easily absorbed through biological membranes and accumulate in fatty tissues.

Another important characteristic is the vapor pressure. Endosulfan sulfate is the least volatile with a vapor pressure of 10−<sup>7</sup> mm Hg, so is more persistent in soil and water. The isomers of endosulfan are semi-volatile, with similar vapor pressures to other chlorinated pesticides, making them susceptible to volatilization to the atmosphere with subsequent atmospheric transport and deposition.

One of the criteria for designing of a chemical as a persistent organic pollutant (POP) is that it has log Kow > 5, both endosulfan isomers and endosulfan sulfate do not exceed this value but are close to it, suggesting a potential for bioaccumulation. The relatively high Koc values indicate a propensity for partitioning to the organic carbon fraction in soils and sediments for both endosulfan isomers and the sulfate [3, 15].


**Table 1.** Physicochemical properties of α-endosulfan, β-endosulfan, and endosulfan sulfate.
