**Effects of Low-Molecular-Weight-Organic-Acids on the Release Kinetic of Organochlorine Pesticides from Red Soil**

Zhao Zhenhua1, Xia Liling2, Wang Fang3 and Jiang Xin3 *1State key laboratory of hydrology-water resources and hydraulic engineering, Hohai University, 2Nanjing Institute of Industry Technology, 3State Key Laboratory of Soil and Sustainable Agriculture Institute of Soil Science, Chinese Academy of Sciences, China* 

#### **1. Introduction**

518 Pesticides in the Modern World - Risks and Benefits

Suchail, S.; Debrauwer, L. & Belzunces, L. P. (2004). Metabolism of imidacloprid in Apis

Sumner, M. E. & Miller, W.P. (1996). Cation Exchange Capacity and Exchange Coefficients. I

ten Hulscher, T. E. M. & Cornelissen, G. (1996). Effect of temperature on sorption

Tomizawa, M. & Casida, J. E. (2003). Selective toxicity of neonicotinoids attributable to

Tomlin, C. (2001). *Pesticide Manual* (10th Revised edition), British Crop Protection Council,

USEPA. (1993). *A Review of Methods for Assessing Aquifer Sensitivity and Ground Water* 

USEPA. (2000). *Standard OperatingProcedures: Soil Sampling*. USEPA, Retrieved from:

Ward, O. P. & Singh, A. (2004). Soil bioremediation and phytoremediation, In: *Applied* 

Wauchope, R. D.; Yeh, S.; Linders, J.;Kloskowski, R.; Tanaka, K.; Rubin, B.; Katayama, A.;

*Management Science*, Vol.58, No.5, (May 2002), pp. 419-445, ISSN 1526-498X Wolt, J. D. (1997). Environmental fate of trifluralin. *Reviews of Environmental Contamination* 

Xue, N.; Yang, R.; Xu, X.; Seip, H. M. & Zang, Q. (2006). Adsorption and degradation of

*Entomology*, Vol.48, (September 2002), pp. 339-364, ISSN 0066-4170

SOPs/Soil%20Sampling/ERTSOP2012%20Soil%20Sampling.pdf>

Springer-Verlag, ISBN 978-3540210207, Berlin, Germany

*&Toxicology*, Vol.153, (May 1997), pp. 65-90, ISSN 0179-5953

Vol.32, No.4, (October 1995), pp. 609-626, ISSN 0045-6535

8561

1526-498X

Wisconsin, USA

ISBN 978-1901396126, Surrey, UK

http://nepis.epa.gov >

ISSN 0007-4861

*Agricultural & Food Chemistry*, Vol.49, No.6, (June 2004), pp. 2899-2907, ISSN 0021-

mellifera. *Pest Management Science*, Vol.60, No.3, (March 2004), pp. 291-296, ISSN

In: *Methods of soil analysis*, D.L. Sparks, (Ed.), pp. 1201-1231, Soil Science Society of America: American Society of Agronomy, ISBN 978-0891188254, Medison,

equilibrium and sorption kinetics of organic micropolutants [Review]. *Chemosphere*,

specificity of insect and mammalian nicotinic receptors [Review]. *Annual Review of* 

*Vulnerability to Pesticide Contamination,* USEPA, Retrieved from: <

<http://www.ecy.wa.gov/programs/eap/qa/docs/QAPPtool/Mod7%20EPA%20

*Bioremediation and Phytoremediation*, A. Singh & O. P. Ward, (Eds.), pp. 1-12,

Kordel, W.; Gerstl, Z.; Lane, M. & Unsworth, J. B. (2002). Pesticide soil sorption parameters: theory, measurement, uses, limitations and reliability [Review]. *Pest* 

benfuracarb in three soils in hunan, people's Republic of China. *Bulletin of Environmental Contamination & Toxicology*, Vol.76, No.4, (April 2006), pp. 720-727, Organochlorine pesticides (OCPs) had been widely used in the world. Due to their strong persistence (The biological half-life period of DDT can reach 10 years in the soil (Li et al., 1999), the biological half-life period of DDE is longer than DDT((ATSDR), 1994)), high enrichment capability and amplification capability and potential high toxicity. They have been banned since the early 1970s in the global scope in succession, and China also banned these pesticides in 1983. After decades of biodegradation, its residual concentration in soil has been reduced significantly (Generally ranges from several to several hundred ng/g). But through the enrichment amplification of food chain, it still has high detection rate in soil, vegetables and human milk. DDE and DDD are the aerobic and anaerobic degradation products of DDT respectively, their insecticidal broad-spectrum and toxicity are higher than the DDT. As a kind of environmental estrogens, it may cause some damage to the health of human body and reproductive system (Maness *et al.*, 1998; Romieu *et al.*, 2000); hexachloroclohexanes (HCHs) have 8 kinds of isomers (*α-,β-,δ-,ε-,γ-,η-,θ-, and l* -HCH), and *γ-*HCH has obvious insecticidal efficacy (ATSDR), 1994). These two types of organochlorine pesticides are typically persistent organic pollutants (POPs).

The solubility of OCPs in water is low and the transference capability of OCPs in the soil is limited, but dissolved organic matter (DOM) in the environment could obviously change the transference behaviour of OCPs, and the predecessor's research mainly focuses on the influence of macromolecular DOM to the migration behaviour of OCPs, and the mechanism lies mainly on its chelation behaviour to OCPs (Chiou *et al.*, 1987; Chiou *et al.*, 2000; Chiou *et al.*, 1986; Hassett & Anderson, 1982; Landrum *et al.*, 1984), studies about the effect of low molecule weight DOM on the retained behaviour of OCPs have rarely seen. In the rhizosphere microenvironment, the existence of low molecular organic acids (LMWOA) of plant root exudates must have great influence on the migration of OCPs, the experiment conducted by White (2003) showed that the seven kinds of low molecular weight organic acid could significantly increase the desorption of p,p'- DDE, the increment could reach at the range of 19%-80% (White & Kottler, 2002; White *et al.*, 2003).

Effects of Low-Molecular-Weight-Organic-Acids on the

rhizosphere relative to the bulk soil. (White *et al.*, 2002).

**2.3 Interaction mechanism between LMWOA and pesticides in soil** 

soil.

Release Kinetic of Organochlorine Pesticides from Red Soil 521

For example, Chen et al. (2007) showed that the measured DDXs in the rhizosphere soils were significantly higher than those in the bulk soils. p,p'-DDT, p,p'-DDD, and p,p'-DDE in the soil accounted for 38%, 47% and 15% of the total. For total DDXs, approximately one third remained on the outer surface of the roots. The partition of DDXs between rhizosphere soil and root surface depended on contaminant affinity to soil organic matter, soil organic matter content and root specific area (Chen *et al.*, 2007), Calvelo Pereira et al. (2006) reported that the roots of *Avena sativa L., Chenopodium spp., Solanum nigrum L., Cytisus striatus (Hill) Roth, and Vicia sativa L.* tended to reduce levels of the HCH isomers in the rhizosphere (Calvelo Pereira *et al.*, 2006),white et al. (2002) found that the chlordane concentration in the rhizosphere (soil attached to roots) was signicantly less than that in the bulk soil. However, the enantiomeric ratio of the chiral components and overall component ratios had changed little in the

LMWOAs have been shown to disrupt the sequestering soil matrix, thereby enhancing the desorption of organic pollutants in soil (White *et al.*, 2003). Consequently, it is expected that LMWOAs, in theory, may affect OCPs availability in soil environment. However, to date, few research has been conducted in this area, and there is limited information on the availability and sorption–desorption behaviour of OCPs from natural soils by organic acids. Gonzalez et al. (2010) showed that sodium citrate and oxalate, at levels usually exuded by plant roots, effectively enhanced desorption of p,p'-DDT, p,p'-DDE and α-cypermethrin, while no effects were observed for α-endosulfan and endosulfan sulfate, the non-ionic surfactant

**2.2 Residual characteristic of organochlorine pesticides in soil and rhizosphere**  Organochlorine pesticides (OCPs) could quickly be adsorbed or bound to the soil or soilorganic matter due to their high hydrophobicity and low water solubility after they were introduced into the soil. With time, the diminishes of these OCPs's bioavailability due to an "aging" effect and the formation of "bound-residues", which takes place during processes of decomposition and humication of organic matter (Alexander, 2000). The residual charactaristics of OCPs in rehizosphere and bulk soil maybe related to the properties of OCPs (water solubility, degradability, volatility,etc.), characteristic of soil mineral (the type and content of organic matter, diameter composition of soil mineral particle, content of oxidationreduction materials, moisture content, etc.), properties of plant (root system characteristic, kind and quantity of root exudates, lipoprotein content, specific surface, etc.) (Alexander, 2000; Calvelo Pereira *et al.*, 2006; Chen *et al.*, 2007; Gonzalez *et al.*, 2005; Inui *et al.*, 2008; Mikes *et al.*, 2009; Mo *et al.*, 2008; Skaates *et al.*, 2005; White *et al.*, 2002; Yang *et al.*, 2008; Yao *et al.*, 2007). For the OCPs with high volatility and relative easy degradation, the concentrations in rehizosphere are generally lower than that in bulk soil, and the results generally appear in the indoor simulation experments. For the OCPs with low volatility and relative harddegradation, the concentrations in rehizosphere are generally higher than that in bulk soil, and the results generally appear in the field experments. The results of pot experiment maybe also differ with field experiment for the same compounds. This kind of contradictory results is mainly due to the pollution sources can be repeatedly inputted by irrigation and dry and wet deposition in field, pollutants would be enrich in rehizosphere with water flow; and the pollution source is single input in indoor simulation experiment, plant absorption or biodegradation result in the concentration of OCPs in rhizosphere soil is lower then in the bulk

The object of this article is to discusses the dynamic release behavior of several organochlorine pesticides like DDT isomer (DDTs) and HCH isomer (HCHs) with LMWOA from variable charge soil (red soil) with self-designed dynamics device, and provide some reference to the migration and fate of these kinds of substances and also the phytoremediation and ecological risk assess ment of organic pollutants in the environment .
