Determination of Paraquat in Several Commercially Available Types of Rice

Introduction: Paraquat (1,1’-dimethyl-4,4’-bipyridine-dichloride) is a herbicide used to combat weeds and improve crop productivity. Its acute toxicity can cause fatal poisoning in humans and animals and several studies have shown a strong correlation between paraquat and Parkinson’s disease. Objective: To determine the concentration of paraquat in different types of rice in Brazil. Method: Paraquat quantification is based on a complexation reaction with sodium dithionite, which generates a blueish color compound, whose absorbance was read in a spectrophotometer at the 600 nm wavelength. Results: Five samples were found to be above the maximum allowed limit, while one sample had a concentration in the upper allowed limit. The method employed did not allow quantification of black rice. Conclusion: There is a need for identification of the type of pesticide used in each examined crop as well as their respective dates of remission in order to improve the safety of agricultural practices.

Food and Nutrition Sciences and space and their seeds can contaminate harvested grains. Some of the most widespread and aggressive weeds are the Echinochloa (rice-grass) species. It has been recorded that infestations of only ten of such weeds per square meter reduced overall yields by 25% [1].
In order to counteract infesting weeds, it is common to use herbicides that block the germination of seeds or the establishment of weed seedlings [2].
Its chronic exposure may lead to carcinogenic processes, especially in relation to pulmonary diseases [6].
Rice is considered the most economically important commodity in many developing countries and it's considered as a basic food source for about 2.4 billion people. It is a crop that shows great adaptability to different soils and climate conditions. Cultivated and consumed on all continents, rice stands out for its production and cultivation area, playing a strategic role, both economically and socially, for the people of the most populous nations of Asia, Africa and Latin America. Compared to other crops, rice stands out second in overall cultivated areas and is surpassed only by wheat. Two main ecosystems are important for consideration of cultivation: the floodplains, which are irrigated by floodwaters; and upland, which are rainfed. These systems encompass all the rice cultivation in the country [8].
As a food with high access to the general population, the National Agency of Sanitary Surveillance (Agência Nacional de Vigilância Sanitária, ANVISA) developed the Program for the Analysis of Agrochemical Waste in food (Programa de Análise de Resíduos de Agrotóxicos, PARA) and 746 rice samples were analyzed. Of these, 715 samples were considered satisfactory, of which 412 did not present detectable pesticide residues among those surveyed and 303 presented residues in concentrations equal to or lower than the maximum residue limit (MRL). In total, 33 different pesticides were detected from 167 analyzed samples [9].
Due to the high rate of rice consumption in Brazil, the objective of this work was to determine quantitatively the amount of paraquat residue in several commercially available types of rice.

Method
This study was carried out in 2018 at the Nucleus of Pharmaceutical Studies of The method used was adapted from the methodology recommended by Pereira and Dantas (1995) [10], which is based on a complexation reaction between paraquat and sodium dithionite, which generates a bluish-colored compound whose absorbance is read in a spectrophotometer at 600 nm wavelength [10] [11].
To obtain the standard curve, a solution containing 0.021 g of paraquat was

Results and Discussion
For the determination of the amount of paraquat in the rice samples, it was necessary to construct a calibration curve that enabled derivation of the linear equation y = 0.803x + 0.0277. The correlation coefficient was determined to be of 0.9958. The absorbance data obtained with the different concentrations of paraquat are been represented in Figure 1.
The calibration curve allowed determination of paraquat concentrations from the rice samples analyzed. Quantified results are been represented in Table 1.
ANVISA guidelines establishes the following limit values for herbicides applied to rice crops either via post-emergency modality or via desiccant application. Maximum Residue Limit (MRL) of 0.5 mg/kg with a 7-day safety interval (time interval between the last application of the pesticide and the harvest or commercialization; for cases of post-harvest treatment, this value represents the time interval between the last application and the commercialization); and the acceptable daily intake (ADI) is 0.004 mg/kg body weight [12].
According to Table 1   above the maximum permitted limit (0.5 mg/kg) and only one sample showed results that were within the upper limit allowed.
The general consumer population should be guaranteed the right to adequate food, proper health and food quality information. The 1988 article 4 of the Federal Constitution provides for food and nutrition security, covering: "promotion of health, nutrition and food for the population; ensuring the biological, health, nutritional and technological quality of food by encouraging healthy eating practices and lifestyles that respect ethnic and racial diversity" [13].   [14].
Generally, herbicides are applied directly to the soil, which is why they come into direct contact with organisms of that environment, among them earthworms, which can metabolically act on residues of these compounds. Using  • Educational and enforcement measures to ensure the use of agrochemicals according to Good Agricultural Practices (GAP); • Residue data that allows assessment of health risk due to exposure to pesticides in food; • Support for re-evaluation of pesticides for decision-making on the restriction and banning of pesticides that are harmful to population health.
However, this initiative needs to be intensified at all levels of the production chain for safety of consumption by the population. It is important to note that paraquat is also a concern at the international level. The United States published the largest number of studies (338), followed by Japan (228) and China (159). The most prevalent topics covered were "acute paraquat intoxication", "paraquat toxic effects to the lungs" and "paraquat toxicity mechanism". Despite being a survey with numerous publications, there is a current need for further investigation related to the consequences of use it in the production line and relative health effects of the populations that consume treated crops in regards to short, medium and long term of consumption. This purpose justifies investing in a broad interest-free research that involves the use of paraquat [17].
Exposure to paraquat is known as a risk factor for the development of neurodegenerative diseases. It is suspected that paraquat can have harmful effects on astrocyte function and such cells of the central nervous system are implicated in the development of and affected in neurodegenerative diseases and brain injuries. A study of the effects of paraquat on the synaptic functions of astrocytes was developed using human astrocytes (HA1800) that were treated separately with paraquat (PQ) at 200, 400 and 800 μmol/L for 12, 24 and 48 hours, respectively. Results obtained showed that paraquat exerts detrimental effects on synaptic functions of astrocytes, which may be involved in the progressive process of neurodegenerative disorders [18].
Crop growers operate under continuous pressures to meet demands of high yield and maximization of profits. However, it is not possible to disregard paraquat's correlation to neurodegenerative diseases and other health problems.
Availability of safe and high-quality foods still has a long way to go in our country. It is essential to develop programs that encourage analysis of pesticide residues, taking into consideration different types of pesticide usage for food production and processing. Furthermore, it is imperative for our country to strengthen the National

Conclusions
There is controversy regarding the release of paraquat as an herbicide, which generates conflicts among regulatory agencies. Paraquat has been implicated in cancer development as well as in neurodegenerative diseases and is therefore a health risk. Alternative non-harmful herbicides should be developed so that paraquat is permanently banned from farming. This argument serves as a base for the implementation of financial incentives towards research and development of alternative health-compliant products. Elimination of paraquat from agricultural practices will most likely impact farmers in regard to crop yields, however, the health of farm workers as well as of the consumer population should be highly prioritized when comparing pesticide usage pros and cons. Intense implementation of continuous and active product inspection should take place prior to commercialization. Furthermore, there's a need to amend the legislation for inclusion of guidelines/requirements that describe pesticide usage and respective grace periods for safe consumption of treated crops.