Pesticide residues in soils planted with Panax notoginseng in south China, and their relationships in Panax notoginseng and soil

Highlights

• 6 pesticides were detected in the P. notoginseng-planted soils of Yunnan Province.

• The median concentrations of six pesticides ranged from 0.24 μg/kg to 46.40 μg/kg.

• The pesticide residues showed in soils never-planted < planted < currently planted.

• A positive correlation of pesticide residues in P. notoginseng and soil was observed.

Abstract

In this study, 73 samples from soils planted with Panax notoginseng and six P. notoginseng samples were collected in Yunnan Province to investigate the residual levels of six pesticides and their relationships with P. notoginseng and soil. All six pesticides were detected in the soils planted with P. notoginseng located in three regions of Shilin, Kaiyuan, and Yanshan. The detection frequencies of the pesticides in the soils followed the order: quintozene (100%) > iprodione (96%) > procymidone (69%) > chlorothalonil (51%) > pyrimethanil (49%) > pyraclostrobin (29%). The median concentrations of iprodione, pyraclostrobin, pyrimethanil, quintozene, procymidone, and chlorothalonil were 46.40, 6.4, 3.1, 2.86, 2.69, and 0.24 μg/kg, respectively. The mean concentrations of pesticides in the three regions followed the order: Kaiyuan > Shilin > Yanshan, except for iprodione. Furthermore, the concentrations of pesticide residues in soils in each region followed the order: soils never planted with P. notoginseng < soils previously planted with P. notoginseng < soils currently planted with P. notoginseng. The concentration of chlorothalonil in P. notoginseng followed the order: root > stem > leaf, whereas those of the other five pesticides followed the opposite order: root < stem < leaf. There were significant positive correlations between the mean concentrations of pesticides in P. notoginseng and those in the corresponding soils. These results indicate that the rational application of pesticides in P. notoginseng cultivation would be effective for reducing the accumulation of pesticides in P. notoginseng to protect people from the harmful effects of residual pesticides.

Introduction

The perennial herb Panax notoginseng F. H. Chen (P. notoginseng), known as Sanqi or Tianqi in Chinese, is generally used to improve the blood circulation, reduce swelling and pain, and treat cardiovascular and cerebrovascular diseases (Li et al., 2009). P. notoginseng has been cultivated for 400 years in the southwest regions of China, but especially in Wenshan, Yunnan Province (Wei and Du, 1996). In general, the roots of P. notoginseng are used as raw materials in Chinese medicinal products. In order to obtain high-quality raw roots, P. notoginseng should be grown in the field for at least 3 years, and this long planting period makes it vulnerable to attacks by many soil-borne pathogens including fungi, bacteria, and nematodes (Wang et al., 1998; Guo et al., 2006; Kim et al., 2006). Thus, pesticides have been widely applied to protect against plant diseases and insect pests during the cultivation of P. notoginseng. Depending on the prevention method and control target, pesticides can be divided into insecticides, fungicides, herbicides, rodenticides, and acaricides (Liu et al., 2018). Fungicides such as iprodione, pyrimethanil, and procymidone are more likely to be applied to P. notoginseng because herbs are prone to fungal diseases during their cultivation and processing (Zhou et al., 2013), which may severely affect the safety of herbal medicines. Moreover, insecticides such as organophosphorus and organochlorine pesticides are used during seed dressing and the plant growing stage to protect against plant diseases and insect damage. For example, quintozene is mainly used to disinfect soil cultivated with ginseng (Zhang et al., 2017). Furthermore, plant diseases and pests are often more severe in temperate and tropical climatic zones, so pesticides are used more frequently in these areas than colder regions, and possibility of pesticide residues in herbal medicines is greater.

At present, there is no standard guidance regarding pesticide usage during herb cultivation in China. Hundreds of Chinese herbal medicines (CHMs) are planted in China, but only a few pesticides have been registered for the control of pests, diseases, and weeds. The lack of an appropriate strategy to provide guidance regarding the application of pesticides and the poor awareness of the safety of pesticides have led to the irrational use of pesticides, widespread crop damage, excessive use of agricultural pesticides, and severe environmental pollution. Considering the potential harm caused by pesticides, many countries have implemented strict maximum residue limit (MRL) regulations for pesticides used in the production of medicinal herbs. For example, the MRL for quintozene (0.1 mg/kg) according to the regulations imposed by China are comparable to or stricter than those regulated in Japan, the European Union, and the USA (Liu et al., 2018). However, only a few registered pesticides are available for preventing diseases that might affect P. notoginseng in China.

Previous studies have reported the detection of pesticide residues in CHMs at high frequencies and several types of pesticides have been identified simultaneously in a single herb (Wong et al., 2010; Hou, 2011; Kuang et al., 2013). The most severe pollution was detected in the plant parts exposed more directly to contact with pesticides, such as the stems, leaves, flowers, and seeds. Furthermore, high levels of pesticide residues have been detected in the roots of some medicinal plants, such as Ginseng Radix et Rhizoma and Notoginseng Radix et Rhizoma. Pesticides are commonly used to treat herbs that are readily damaged by plant pests and diseases, such as Lycium barbarum and P. notoginseng. However, the irrational use of pesticides to protect herbs from plant diseases and insect damage can lead to severe contamination of herbal medicines and the soil environment. The pesticide residues found in soils are mainly derived from their direct application and some pesticides can remain stable in the environment. Soil contamination with pesticides such as organochlorines, organophosphates, carbamates, triazines, ureas, and triazoles has also been investigated in agricultural areas in many countries throughout the world (Gonçalves and Alpendurada, 2005; Jiang et al., 2009; Park et al., 2011; Pose-Juan et al., 2015). Most fruits, vegetables, cereals, and herbs are planted in soil, so the presence of residual pesticides in soil is likely to have negative effects on human health following exposure to residues in food (Liu et al., 2016a, Liu et al., 2016b). Several studies have investigated the relationships among pesticide residues in plants, the edible parts of plants, and the soils used for their cultivation (Ding et al., 2014; Mantzos et al., 2016; Mitton et al., 2016), but few have studied the pesticide residues found in the soils used for herb production.

To the best of our knowledge, little information is available about the residual levels of fungicides and insecticides in soils planted with P. notoginseng. Thus, in order to ensure the safety of P. notoginseng and promote its import and export, it is necessary to investigate the pesticide residues in soils planted with P. notoginseng, and to determine the relationships among pesticide residues in soils and P. notoginseng. Therefore, in the present study, we determined the residue levels of widely used pesticides in P. notoginseng and samples of soil used for planting P. notoginseng collected from different regions of Yunnan province. The correlations among pesticide residues in P. notoginseng and soils were investigated in order to provide theoretical guidance regarding the rational application of pesticides during the cultivation of P. notoginseng in the south of China.