8-Hydroxyquinoline (8HQ) compounds have been reported to possess diverse bioactivities. In recent years, drug repositioning has gained considerable attention in drug discovery and development. Herein, 8HQ (1) and its derivatives (2–9) bearing various substituents (amino, nitro, cyano and halogen) were investigated for their antimicrobial against 27 microorganisms (agar dilution method) and antioxidant (DPPH method) activities. The parent 8HQ (1) exerted a highly potent antimicrobial activity against Gram-positive bacteria including diploid fungi and yeast with MIC values in the range of 3.44–13.78 μM. Moreover, the halogenated 8HQ, especially 7-bromo-8HQ (4) and clioquinol (6), displayed a high antigrowth activity against Gram-negative bacteria compared with the parent compound (1). Apparently, the derivatives with a relatively high safely index, e.g., nitroxoline (2), exhibited strong antibacterial activity against Aeromonas hydrophila (MIC=5.26 μM) and selectively inhibited the growth of P. aeruginosa with the MIC value of 84.14 μM; cloxyquin (3) showed a strong activity against Listseria monocytogenes and Plesiomonas shigelloides with MIC values of 5.57 and 11.14 μM, respectively. Most compounds displayed an antioxidant activity. Specifically, 5-amino-8HQ (8) was shown to be the most potent antioxidant (IC50=8.70 μM) compared with the positive control (α-tocopherol) with IC50 of 13.47 μM. The findings reveal that 8HQ derivatives are potential candidates to be further developed as antimicrobial and antioxidant agents.

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BackgroundThe wide use of pesticides raises concerns on the health risks associated with pesticide exposure. For developing countries, like Thailand, pesticide monitoring program (in vegetables and fruits) and also the maximum residue limits (MRL) regulation have not been entirely implemented. The MRL is a product limit, not a safety limit. The MRL is the maximum concentration of a pesticide residue (expressed as mg/kg) recommended by the Codex Alimentarius Commission to be legally permitted in or on food commodities and animal feeds (Codex Alimentarius Commission, 2015; European Commission, 2015). MRLs are based on supervised residue trial data where the pesticide has been applied in accordance with GAP (Good Agricultural Practice). This study aims at providing comparison data on pesticide residues found in three commonly consumed vegetables (Chinese kale, pakchoi and morning glory) purchased from some local markets and supermarkets in Thailand.MethodsThese vegetables were randomly bought from local markets and supermarkets. Then they were analyzed for the content of 28 pesticides by using GC-MS/MS.ResultsTypes of pesticides detected in the samples either from local markets or supermarkets were similar. The incidence of detected pesticides was 100% (local markets) and 99% (supermarkets) for the Chinese kale; 98% (local markets) and 100% (supermarkets) for the pakchoi; and 99% (local markets) and 97% (supermarkets) for the morning glory samples. The pesticides were detected exceeding their MRL at a rate of 48% (local markets) and 35% (supermarkets) for the Chinese kale; 71% (local markets) and 55% (supermarkets) for the pakchoi, and 42% (local markets) and 49% (supermarkets) for the morning glory.DiscussionThese rates are much higher than those seen in developed countries. It should be noted that these findings were assessed on basis of using criteria (such as MRL) obtained from developed countries. Our findings were also confined to these vegetables sold in a few central provinces of Thailand and did not reflect for the whole country as sample sizes were small. Risk assessment due to consuming these pesticide contaminated vegetables, still remains to be evaluated. However, remarkably high incidence rates of detected pesticides give warning to the Thai authorities to implement proper regulations on pesticide monitoring program. Similar incidence of pesticide contamination found in the vegetables bought from local markets and supermarkets raises question regarding the quality of organic vegetables domestically sold in Thailand. This conclusion excludes Thai export quality vegetables and fruits routinely monitored for pesticide contamination before exporting.

Objectives The wide use of pesticides raises serious concerns regarding food safety and environmental impacts. There is increasing public concern about the potential health risks linked with exposure to pesticides. Regulation of maximum residue limits (MRL) of pesticide residues in food commodities has been established in many developed countries. For developing countries, like Thailand, this regulation often exists in law, but is not completely enforced in practice. Thus, pesticide residue levels in vegetables and fruits have not been thoroughly monitored. The present study aimed to examine potential health risks associated with pesticide exposure by determining the pesticide residues in two commonly consumed fruits, watermelon and durian. Methods The fruit samples were purchased from markets in central provinces of Thailand and assayed for the content of 28 pesticides. Analysis of pesticides was performed by multiresidue extraction and followed by GC-MS/MS detection. Results Of 28 pesticides investigated, 5 were detected in 90.7 % of the watermelon samples (n = 75) and 3 in 90 % of durian samples (n = 30). Carbofuran, chlorpyrifos, diazinon, dimethoate and metalaxyl were found in watermelons, whereas dichlorvos, dimethoate and metalaxyl were detected in durians. However, their levels were much lower than the recommended MRL values. Conclusions These pesticide levels detected in the fruits are unlikely to harm the consumers; therefore it is safe to eat watermelon and durian in Thailand. While our results found negligible risk associated with pesticide exposure from consuming these common tropical fruits, special precautions should be considered to decrease total exposure to these harmful pesticides from various foods.

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