Legacy and Current-Use Insecticides in Agricultural Sediments from

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Legacy and current-use insecticides in agricultural sediments from South China: The impact of application pattern on the occurrence and risk Yanli Wei, Huizhen Li, Junjie Zhang, Jingjing Xiong, Xiaoyi Yi, and Jing You J. Agric. Food Chem., Just Accepted Manuscript • Publication Date (Web): 11 May 2017 Downloaded from http://pubs.acs.org on May 16, 2017

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Journal of Agricultural and Food Chemistry

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Legacy and current-use insecticides in agricultural sediments from South

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China: The impact of application pattern on the occurrence and risk

3 Yanli Weia,b, Huizhen Lib, Junjie Zhangb, Jingjing Xionga,b,c, Xiaoyi Yia,c, Jing Youb,*

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a

State Key Laboratory of Organic Geochemistry, Guangzhou Institute of Geochemistry, Chinese

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Academy of Sciences, Guangzhou 510640, China b

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and Guangdong Key Laboratory of Environmental Pollution and Health, Jinan University,

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School of Environment, Guangzhou Key Laboratory of Environmental Exposure and Health,

Guangzhou 510632, China c

University of Chinese Academy of Sciences, Beijing 100049, China

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*

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Tel: 0086-20-8522-6326, Email: [email protected]

Corresponding author.

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1

ACS Paragon Plus Environment


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ABSTRACT Legacy and current-use insecticides were analyzed in sediments collected from a typical

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rice planting region in South China. Total concentrations of insecticides varied from 1.63 to 775

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ng g-1 with mean and median values of 67.0 and 11.5 ng g-1, respectively. Pyrethroids

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predominated pesticide composition (31.7%), followed by organophosphates (23.0%) and

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fiproles (20.8%). Sediment risk analysis showed that pyrethroids, fiproles and abamectin posed

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significant risk to benthic invertebrates in one-third of sediments. Different distribution of

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pyrethroids and organophosphates in urban and agricultural areas was consistent with their

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application patterns, while legacy OCPs showed no region-specific distribution because of rapid

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transition of land use pattern from agricultural to urban areas. Likely illegal use of pyrethroids

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and fipronil caused serious ecological risks in agricultural waterways. Pyrethroids and fipronil

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were restricted to use in paddy field but their occurrence and risk in agricultural waterways were

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high, calling for better measures to regulate the illegal use of insecticides.

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Keywords: Agricultural waterways; Sediment; Legacy and current-use insecticides; Risk; Application pattern

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INTRODUCTION Pesticides are released into the environment in large quantities due to their intensive use in

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both agricultural and urban areas. Owing to their high biological activity, insecticides are

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regarded as one of the key stressors jeopardizing freshwater biodiversity and ecosystem

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functioning on a global scale.1, 2 Pesticide pollution is a global issue, yet studies on the

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occurrence and risk of insecticide residues in aquatic ecosystems are largely limited in developed

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countries.3, 4 Little information is available in developing countries, but insecticide-induced risk

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to aquatic ecosystems in these regions should not be ignored, particularly in countries with

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intense agricultural activities and urbanization.5, 6 As the world's most populous nation, China

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has been facing tremendous challenges to balance the benefit and risk of agricultural use of

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pesticides. Overuse and abuse of pesticides make the case even worse.7, 8

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With continuously increasing demand for pesticides worldwide, application pattern of

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insecticides has shifted over time.9, 10 New generations of insecticides, such as organophosphate

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insecticides (OPs, e.g. chlorpyrifos), pyrethroids (e.g. cypermethrin), phenylpyrazoles (e.g.

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fipronil) and biopesticides (e.g. abamectin) have been developed to replace legacy insecticides

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(e.g. organochlorine pesticides (OCPs)). Legacy OCPs, like hexachlorocyclohexanes (HCHs)

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and dichlorodiphenyl trichloroethane (DDT) are highly persistent, resulting in their co-

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occurrence with current-use pesticides (CUPs) in the environment though they have been banned

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for use decades ago.11

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Many insecticides are hydrophobic and tend to accumulate in sediment, posing a threat to

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benthic organisms. Therefore, it is imperative to monitoring sediment-associated insecticides.

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Previous studies on pesticide residues in aquatic environment in China mostly focused on OCPs,

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especially HCHs and DDTs.6, 11 Recently, researchers started to pay attention to ecological risk

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of sediment-associated CUPs in China, yet most studies were conducted in urban settings.5, 12, 13

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Information on CUP residues in agricultural waterway sediments in China was less known.9 In

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China the most use of pesticides in agriculture was for grain production, accounting for 68% of

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the total agricultural demand for pesticides, which was significantly higher than those for

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commercial crops (15%), vegetables (11%) and tea and fruits (5.3%).14 Wang et al. 15 analyzed

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CUPs in sediment in a Chinese lake receiving water from both agriculture and urban areas and

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found OPs in lake sediments were mainly originated from agricultural use while pyrethroids

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from urban runoff. Sun et al.9 found the historical profiles of insecticide composition in sediment

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cores from agricultural and urban areas were significantly different. These studies suggested that

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distinct application patterns of insecticides in agricultural and urban areas may result in different

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insecticide risks in aquatic ecosystems.

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The objectives of the present study are to evaluate the occurrence and composition of a

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battery of legacy and current-use insecticides in agricultural waterways in South China and better

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understand the impact of application pattern on ecological risk of insecticide residues in

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sediment. To achieve the goals, several classes of insecticides were analyzed in sediments

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collected from a watershed mainly serving for rice planting practice. The composition,

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distribution and risk of sediment-bound insecticides were assessed. At last, data from the present

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study and the literature were compared by classifying the sampling sites into three categories,

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namely agricultural, mix-land (agricultural mixed with urban) and urban areas.

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MATERIALS AND METHODS Study Area and Sediment Collection. Rice planting is the main agricultural practice in South China where pesticide application rate ranks the top in China.6 A sampling campaign was

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conducted in September 2014 and 23 surface sediment samples (0–5 cm) were collected from

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agricultural waterways (ditches and streams) which received water from rice planting fields in

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Shanghang and it adjacent area, Fujian, South China (Fig. 1). The coordinates and description for

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sampling sites are presented in Table S1 (“S” represents figures and tables in the Supporting

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Information thereafter).

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Based on the distance from sampling sites to the nearest rice field, the sampling waterways

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were defined as ditches (distance < 5 m, D1–D6) and streams (distance > 5 m, S1–S17).

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Sediment samples were collected using a shovel by wading into the water in the depositional

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zones, sieved with a 425 µm sieve for removing large debris, stored in ice, transported to the

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laboratory and kept at -20 oC in darkness. After removing the inorganic carbonates using 1 mol/L

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HCl, the contents of total organic carbon (TOC) of sediment samples were analyzed using a

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Vario EL III Elemental Analyzer (Hanau, Germany).

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Chemical Analysis. A total of 40 insecticides were analyzed in sediment samples (Table

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S2). After adding the surrogate standards (4,4’-dibromooctafluorobiphenyl (DBOFB), 13C-

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polychlorinated biphenyl (PCB)-141 and PCB-209) to sediment samples, OCPs, OPs,

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pyrethroids and fiproles (fipronil and its degradation products, fipronil sulfide and fipronil

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sulfone) were extracted from sediments using ultrasound-assisted microwave extraction, and the

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extracts were cleaned with solid phase extraction cartridges. The target analytes were analyzed

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on an Agilent 7890-5973 and a Shimadzu QP-2010 plus GC/MS upon the addition of the internal

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standards (PCB-24, PCB-82, PCB-189, parathion-d10 and trans-cypermethrin-d6). Meanwhile,

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abamectin and emamectin benzoate (ABAs) in sediment were extracted with ultrasound

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extraction and analyzed on a Shimadzu DGU-30A and AB SCIEX TRIPLE QUADTM 5500

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HPLC/MS/MS and clothianidin-d3 and imidacloprid-d4 were used as the surrogate and internal

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standard for ABAs, respectively. Detailed procedures for sample preparation and chemical

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analysis are provided in the Supporting Information and HPLC/MS/MS conditions including

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precursor ions, product ions, collision energy and retention time of ABAs are shown in Table S3.

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Quality Assurance and Quality Control. The instrument was checked with a calibration

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standard every 10 injections and the variation of each analyte was within 20%. Two sets of

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quality assurance and quality control samples were analyzed along with the 23 samples,

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including a procedural blank, a matrix blank, and three matrix spiked samples. The performances

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of analytical procedures were checked with quality control samples. The concentrations of

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individual insecticides in blank sample were all less than the lowest concentration of the

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calibration standards. The recoveries for OCPs, OPs, pyrethroids, fiproles and ABAs in the

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spiked samples were 95 ± 28%, 84 ± 36%, 86 ± 25%, 79 ± 16% and 80 ± 37%, respectively. The

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recoveries (mean ± standard deviation) of the surrogates in all samples were 62 ± 14%, 81 ±

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12%, 93 ± 17% and 99 ± 11% for DBOFB, 13C-PCB-141, PCB-209 and clothianidin-d3,

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respectively.

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Data Analysis. The sum concentrations of 15 OCPs, 9 OPs, 11 pyrethroids, 3 fiproles and

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2 ABAs were defined as Σ15OCP, Σ9OP, Σ11PYE, Σ3FIP and Σ2ABA, respectively. The

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concentrations of insecticides in sediment are presented on a dry weight basis thereafter unless it

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is pointed out to be TOC-based. The reporting limits (RLs) were defined as the lowest

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concentration of standards used in the calibration curves multiplied by the final volume of the

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extract and then divided by the dry weight of extracted sediment (5 g). The lowest concentrations

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of the calibration standards and final volumes of the extract were 10, 5 and 5 ng mL-1 and 100,

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500 and 100 µL for individual OCPs, ABAs and other insecticides, respectively. Accordingly,

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the RLs were calculated as 0.2, 0.5 and 0.1 ng g-1 dry weight for individual OCPs, ABAs and

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other insecticides, respectively. Half of the RL was used for calculating the sum concentrations

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and composition of individual class of insecticides when an insecticide was found in sediment at

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a concentration less than the RL.

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Significance in pesticide concentrations among sampling sites was determined using one-

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way analysis of variance. Welch’s t-test was used for the comparison between two sets of

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samples with unequal variances in the present and previous studies. The criterion of significance

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was defined as p < 0.05 in all statistical analyses.

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Pesticide toxicity index for sediment (sediment-PTI) has been proposed as a quantitative

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indicator to evaluate the risk of sediments contaminated by multiple pesticides and it is

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calculated using equation 1. 16

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Cp    Sediment-PTI = (sum-LEBQ or sum-TEBQ) = ∑ np =1   LEB or TEB 

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Where Cp is the TOC-normalized concentration of a pesticide p (µg g-1 OC) and n is the

(1)

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number of detected pesticides in a sediment sample. The likely effect benchmark (LEB, µg g-1

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OC) defines the concentration of a pesticide in sediment above which there is a high probability

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of adverse effects to benthic invertebrates, and threshold effect benchmark (TEB, µg g-1 OC) is

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the concentration below which adverse effects of a pesticide are unlikely happened. The Q in

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LEBQ and TEBQ stands for quotients. Thus, LEBQ of individual or sum pesticides higher than 1

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indicates likely causing adverse effects, and TBEQ value lower than 1 indicates no adverse effect

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to benthic organisms.

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RESULTS A variety of insecticides were detectable in waterway sediments from the rice planting area and the concentrations of individual OCPs, OPs, pyrethroids, fiproles and ABAs are shown in

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Tables S4–S7, respectively. As summarized in Table 1, the total insecticide concentrations

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varied site by site from 1.63 to 775 ng g-1 with mean and median values of 67.0 and 11.5 ng g-1,

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respectively. In general, insecticide concentrations were higher in the ditches than the streams

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and the highest concentration of insecticides was detected in sediment D6 followed by D5 and

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D4 (Fig. 2a).

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The composition of individual classes of insecticides varied significantly among sites (Fig.

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2b). Pyrethroids were the most dominant insecticides in 39% of the sediment samples and

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accounted for 31.7% of the total insecticide abundance on average, followed by OPs (23.0%),

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which were the most abundant insecticides in four sediments (D1, D2, S3 and S10).

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Occasionally, OCPs and fiproles had sediment concentrations greater than pyrethroids and OPs

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in some sites, contributing 12.5% and 20.8% to the sum insecticide concentrations, respectively.

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The average contribution of ABAs to the sum insecticide abundance (12.0%) was similar to

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OCPs, but they never dominated insecticide composition in any sediment. Individual insecticides

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within the same class also showed distinct composition pattern among sediments and the

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occurrence and composition of individual classes of insecticides are discussed below by

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chemical class.

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OCPs. As shown in Table S4, sediment concentrations of Σ15OCP were from not-detected (nd) to

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476 ng g-1, with the highest one at site D6. Less than three OCPs were detected in a single

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sediment except for S13 which contained six OCPs. The majority of OCPs were detected in less

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than four of the 23 sediments while a-chlordane and p,p'-DDE were detectable in 10 and 18

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sediments, respectively. Sediment concentrations of a-chlordane were all

Legacy and Current-Use Insecticides in Agricultural Sediments from

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