Evaluating the Presence of Pesticide Residues in Organic Rice Production in An Giang Province, Vietnam

Hay V. Duong2,3,*, Thanh C. Nguyen1,*, Xuan T. Nguyen1, Minh Q. Nguyen1, Phuoc H. Nguyen1 & Tanh T. Vo1 1 Asian Organic Agriculture Research and Development Institute (AOI), Ho Chi Minh City, Vietnam 2 Department of Agronomy, Institute of Agricultural Sciences for Southern Vietnam, Ho Chi Minh, Vietnam (IAS) 3 Department of Agriculture Chemistry, Jeonbuk National University, Jeollabuk-do, South Korea


Introduction
Pesticides in controlling rice diseases have increased in recent years due to the higher incidence of insects and pests. However, pesticide residues in food are a major public health concern and harm producers and consumers (Hou et al., 2013). Identifying the presence of such residues in all types of food (both fresh and industrialized) is important to guarantee food safety (Wang et al., 2012). At the same time, the use of pesticides on rice fields can affect the quality of environmental resources such as groundwater and surface water.

Studied Pesticides and Rice Cultivation
The study pesticides were selected according to the audit program of the organic certification body, ControlUnion (CU). The total number of investigated pesticides was 854 substrates (Appendix 1). Rice varieties grown in these studied areas were Hong Ngoc Oc Eo and ST 25, having a growing duration of 95 days and 114 days, respectively. Both varieties belong to the Oryza sativa species. In the organic production model, farmers were trained in organic rice cultivation that as described by Hay et al. (2018). Paddy was sowed and then constantly flooded with 5-7 cm depth from soil surface still 1 month before harvesting.

Sampling
Irrigation water, soil, and plants were sampled at the drought stage (around 20 days before harvest). Water samples were collected in 1 L plastic bottles, soil samples were collected at a depth of 0−10 cm, and plant samples were collected by chopping the above ground portion of the plants. The collection of soil, water, and rice samples should accurately represent the entire production batch and target to detect residual chemicals thoroughly at high-risk areas (different from random sampling). The number of samples depends on the farming conditions of each household group and risk capacity. If farming conditions of the household is not good with high-risk possibility, samples need to be taken more. If the number of households is too large, take at least 10% (Singh and Masuku, 2014). Each sample was collected from neighboring households and then mixed as 1 sample for analysis. A total number of 15 samples was sampled and analyzed during three years (2019 -2021).

Pesticide Analysis
The samples were sent for analysis at the labs designated by CU. Without washing, the samples were then extracted and analyzed using GC-MS/MS, which was described by Braun et al. (2018) and LC-MS/MS described by Shah et al. (2015). The results from the analyses were reported in parts per million (ppm) or milligram per kilogram (mg kg -1 ).

Evaluating Criteria and Statistical Analysis
In this study, we use the criteria to evaluate the presence of pesticides as follows. Limit of detection (LOD) is the lowest quantity of an active ingredient that can be distinguished from the absence of active ingredients. Pesticide concentration (PC) (mg kg -1 ) is an amount of pesticide's active ingredient per total weight of the sample. Progressive presence (PP) is the cumulative number of impressions from previous times. Frequency of occurrence (FOO) is the number of times that pesticide detected with a concentration higher than LOD. Contamination rate (CR) (%) is determined by the percentage of frequency of occurrence per the total number of samples. Microsoft Excel was used for data analysis and graphing.

Pesticide Residues Were Present in Soil and Rice Samples in Organic Rice Fields of An Giang Province
A total number of 15 samples, including 13 rice samples, 1 soil sample, and 1 water sample, was analyzed during three years of project implementation. The results showed that 16 pesticide types were found in the samples, including tricyclazole, chlorpyrifos, isoprothiolane, difenoconazole, propiconazole, hexaconazole, chlorfenapyr, azoxystrobin, and cypermethrin, metalaxyl & metalaxyl-M, paclobutazol, niclosamide, chlorfenson, fipronil, fipronil-desulfinyl, and fenoxanil with concentrations from 0.005 mg kg -1 to 0.71 mg kg -1 (Table 1). Among the analyzed samples, sample No. 7 was the most contaminated, with 11 detected substances, while samples No. 2 and No. 15 were free of pesticide residues, and sample No. 9 only detected chlorpyrifos. This result indicates that different samples from different households found various contaminants in the same organic production model (i.e. leakage from neighboring fields were being controlled). We can infer that the contaminated pesticides came from two sources. The first, the pesticides came from a passive way, in which pesticides have been used in previous crops and are still remained up to the time of sampling. This correlates with several studies, which reported that pesticide persistence in the environment was determined by a measure known as the half-life or time for starting material to be reduced by 50%, where the half-life of pesticides can range from several hours up to 4-5 years (Hanson, 2015). Therefore, pesticides with high half-lives in soil (above 60 days), such as tricyclazole (305 days) (Thai et al., 2009), propiconazole (315 days) (Garrison et al., 2009(Garrison et al., , 2011, hexaconazole (69.3 and 86.6 days) (Maznah et al., 2015), and isoprothiolane (9.4 months) (Suzuki et al., 1998) can come in passive ways, such as pesticide residues detected in sample No. 1,No. 5,and No. 11. The second, pesticides with short soil half-lives such as fenoxanil (3.3-4.4 days) (Fu et al., 2016), azoxystrobin (7.5 days) (Gajbhiye et al., 2011), cypermethrin (0.5-8 weeks) (Paul, 2005) and chlorpyrifos (18.7 and 13.9) (Hwang et al., 2018) might actively be applied by farmers. high-risk group has pesticides with a contamination rate greater than 50%, including only tricyclazole (80%). The medium-risk group is those with contamination rate ranged from 10% to 50%, including chlorpyrifos (47%), isoprothiolane (47%), difenoconazole (40%), propiconazole (40%), hexaconazole (40%), chlorfenapyr (33%), azoxystrobin (20%), and cypermethrin (20%). The low-risk group is those with a contamination rate of less than 10%, including metalaxyl & metalaxyl-M, paclobutazol, niclosamide, chlorfenson, fipronil, fipronil-desulfinyl, and fenoxanil, detected with a contamination rate of 7% (Fig. 2). Among them, tricyclazole was the most prominent with a contamination rate of 80%. This is reasonable because tricyclazole (5-methyl-1,2,4-triazolo[3,4b]benzothiazole) is a unique fungicide to control rice blast disease caused by the fungus Pyricularia oryzae (Peterson, 1990). It is worth noting that among these 16 active substances, there are substances such as chlorpyrifos and fipronil that have been prohibited from use by the Ministry of Agriculture and Rural Development (MARD, 2019). Abroad, the use of some fipronil-based products in domestic animals has not been recommended for a long time (Colin et al., 2003). Compared to other research on pesticides assessment in Mekong Delta, Berg (2001) reported that 64 different pesticides were used in rice and rice-fish farms of the Mekong River delta. Therein, five pesticides, including propiconazole, hexaconazole, isoprothiolane, cypermethrin, and fipronil, are matched with the result of this study. A decade after that, another study by Berg and Tam (2012) reported that twenty pesticides used most in rice-fish farms by farmers in Tien Giang and Can Tho provinces in 2007, in which seven of them are matched with this discussing result, including propiconazole, hexaconazole, isoprothiolane, tricyclazole, cypermethrin, fipronil, and chlorpyrifos. Along with that, the study on pesticides and antibiotics in permanent rice, alternating rice-shrimp and permanent shrimp systems of the coastal Mekong Delta, Vietnam by Braun et al, (2019) reported that analyzed chemicals comprised 12 pesticides most commonly used in rice paddies, among them seven pesticides are found in this study, including chlorpyrifos, fipronil, difenoconazole, propiconazole, hexaconazole, isoprothiolane, and azoxystrobin. Summarizing the previous researches and this study we can infer that propiconazole, hexaconazole, isoprothiolane, and fipronil were the main contaminated pesticides in rice production in An Giang province in detail and Mekong River delta in general for more than two decades.
In this study, among 16 detected substances, there were 7 insecticides, 7 fungicides, 1 snail killer, and 1 growth regulator (Table 2). We can realize that various types of pesticides were detected in organic rice fields. This is more evidence to prove that farmers had broken the rules in organic production to apply pesticides in their fields, which agrees with Nguyen and Van's report (2021).
Research results serve as the basis for pre-inspecting raw material areas for organic rice production to reduce risks, analysis, and evaluation costs. We recommend that the provincial, national, and international organizations increase funding support for AOI researchers to organize and build the linkage models in rice value chains according to organic standards in the rice-intensive farming areas to minimize the application of harmful pesticides in the environment.

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