Remediation of DDT‐contaminated soil using optimized mixtures of surfactants and a mixing system

Abstract

Soil contaminated with persistent pesticides, such as DDT, poses a serious risk to humans and to wildlife. A surfactant-aided soil-washing technique was studied as an alternative method for remediation of DDT-contaminated soil. An ex situ soil washing method was investigated using nonionic and anionic surfactants due to the clayey structure of the contaminated soil. A mixture of 1 percent nonionic surfactant (Brij 35) and 1 percent anionic surfactant (SDBS) removed more than 50 percent of DDT from soil in a flow-through system, whereas individual surfactants or other combinations of the surfactants had a lower removal efficiency. The soil-washing technique was improved using a mixing system. The mixture of surfactants was optimized in the mixing system, and the combination of 2 percent Brij 35 and 0.1 percent SDBS was found to be optimum, removing 70 to 80 percent of DDT. Prewashing of the soil with tap water decreased the adsorption of surfactants INTRODUCTIONIn many locations in Canada and elsewhere around the world, soil contamination represents a serious risk to both humans and the environment (Harris et al., 2000). Contamination with organochlorines is considered to be of particular importance since organochlorines are persistent substances that may represent a continuing source of contamination for decades. Among the organochlorines, dichloro-diphenyl-trichloroethane (DDT) is one of the most notorious synthetic pesticides since it continues in use to this day, although use of DDT has been widely restricted in application since 1972 (Hitch & Day, 1992;Martijn et al., 1993;Turusov et al., 2002). Concerns with worldwide spraying of DDT eventually led to use of DDT being banned in most countries in 1972. Also, DDT was subsequently banned for agricultural use worldwide, but its limited use in disease vector control continues to this day in some parts of the world (Vieira et al., 2001).DDT and its metabolites-breakdown or by-products of DDT, including 1,1-dichloro-2,2-bis(p-chlorophenyl)ethane (DDD) and 1,1-dichloro-2,2-bis(p-chlorophenyl) ethylene (DDE)-are extremely persistent in the environment and may accumulate in the food chain (Veith et al., 1979) 119 Remediation of DDT-Contaminated Soil Using Optimized Mixtures of Surfactants and a Mixing Systemhealth, and they are known carcinogens (Kashyap et al., 1977). As a consequence, lands contaminated with DDT are limited in their development potential (e.g., change of land use from agricultural to residential may be disallowed). It is highly likely, for example, that significant expanses of agricultural land continue to have levels of DDT and its metabolites that are elevated in concentration, although only limited testing has been carried out to date. Environmental agencies, such as the U.S. Environmental Protection Agency and the Ontario Ministry of the Environment (MOE), have established standards and guidelines, exceedance of which precludes specific land use. Hence, due to the long half-life of DDT and its metabolites in natural environmental conditions, co...

Remediation of DDT and Its Metabolites in Contaminated Sediment

“…The desirable characteristics of a surfactant in sediment washing are the following: biodegradable and soluble at ambient temperature at the time of sediment processing, low toxicity, low sorption to sediment, low surface tension, and low cmc level. Ghazali et al [42] reported that a mixture of Brij 35, a nonionic surfactant, and sodium dodecyl benzene sulfonate, an anionic surfactant, was more effective than individual surfactants in removing DDTR. Wash-off liquids containing DDTR are treated (dechlorinated) in the next step using different methods, such as degradation using zero-valent iron under anaerobic conditions [86], reduci n g a g e n t s ( c y s t e i n e o r s o d i u m s u l f i d e ) , o r photodechlorination reaction [19].…”

Sorption/desorption of 1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane(4,4′-DDT) on a sandy loam soil

“…Wenzel et al (2002) and Sun et al (2009) found that soils with a higher organic fraction would bind more DDT. However, others have reported that clays could have a major influence on sorption (Dai et al 2008;Ghazali et al 2010).…”

“…Aged activated carbon sorbed up to 10 % more than freshly spiked carbons (Oen et al 2011). Soil parameters affecting desorption of DDT were stated to be % organic matter, amount of dissolved organic carbon, surface area, % clay/silt, and pH levels (Ghazali et al 2010;Holoubek et al 2009;Oen et al 2011;Thangavadivel et al 2011). For instance, relatively low pH values (pH=5.4) were said to cause stronger hydrogen bonding when compared to neutral or alkali pH conditions (Boivin et al 2005;Thangavadivel et al 2011).…”

“…Another adverse effect on human health is that it is an endocrine disruptor and a suspected carcinogen (Fang et al 2012;Holoubek et al 2009; Thomas and Gohil 2011). Experimental studies on animals have shown that DDT and its two most frequently observed metabolites dichlorodiphenyldichloroethylene (DDE) and dichlorodiphenyldichloroethane (DDD) have neurotoxic, carcinogenic, immunotoxic, estrogenic, and reproductive effects (Ghazali et al 2010;Nadeau et al 1998; Van den Berg 2009). Studies have reported half lives to be from 2-15 years to >20 years (Corona-Cruz et al 1999;Ricking and Schwarzbauer 2012;Zhao et al 2010;Zhou et al 2011).…”

Formation and Fate of Point-Source Nonextractable DDT-Related Compounds on Their Environmental Aquatic-Terrestrial Pathway

“…DDT is associated with serious risks to the environment and human health, including carcinogenesis, endocrine disruption, and estrogenic action. , However, DDT and its metabolites (DDXs), particularly dichlorodiphenyldichloroethane (DDD) and dichlorodiphenyldichloroethylene (DDE), which could be the congeneric impurities of technical DDT at very low amounts, − are still frequently worldwide detectable in considerable amounts even decades after the DDT prohibition . Those metabolites are also reported to be environmentally and biologically harmful. − The ongoing usage of the DDT related pesticide dicofol, as well as specialty applications of DDT in antifouling paints and limited disease vector control efforts, result in substantial emission of DDT/DDXs that are cause for continued environmental concern. , Consequently, knowledge on nonextractable DDXs is still necessary for both risk assessment and remediation actions.…”