Our results demonstrated that the health effects of different pesticides were different. In general, the adverse health effect of insecticide use was severer than that of the uses of herbicides and fungicides. Glyphosate use was not associated with farmer health damage, while the use of non-glyphosate herbicides inclined to induce renal dysfunction and decrease of serum folic acid. Moreover, chemical lepidopteran insecticides were likely to damage hepatic function, increase serum glucose level and induce the inflammation. It is notable that agricultural use of chemical lepidopteran insecticides might also induce severe damages to peripheral nerves. In contrast, there was not any association between farmer health and the uses of biological lepidopteran and non-lepidopteran insecticides. Additionally, fungicide use probably damaged hepatic function and induced the loss of vitamin B 12 . Given that the adoption of GM glyphosate-tolerant crops can sharply reduce the uses of other herbicides in spite of increasing glyphosate use, and adoption of GM insect-resistant crops can significantly reduce the use of chemical lepidopteran insecticides18,19,20,21,22,23,24,25, our results implied that the alterations in pesticide use are likely to benefit farmer health if GM crops can be adopted by farmers in China and globe.

Agricultural herbicide use, in this study, was only second to insecticide use, and glyphosate accounted for about half of the total use of herbicides (Table 1). As shown, glyphosate use was not likely to induce negative effect on the blood chemistry panel. It was consistent with the previous studies of human occupational exposure29,30, but out of accord with the animal studies47,48,49,50. It might be attributed to that the relative level of glyphosate intake of the occupational exposed humans was less than that of the oral-administrated experimental animals, and far from enough to induce human health damage. In comparison, the use of non-glyphosate herbicides inclined to increase the risks of renal dysfunction and decrease of serum folic acid. Similar findings were previously published31,32,33. For example, exposures to paraquat, atrazine and acetochlor were associated with renal function damage in both animals and humans31,32,33. Note that these three herbicides were among the most common used ones second to glyphosate in this study. Moreover, we also found that neither glyphosate nor non-glyphosate herbicides uses were associated with peripheral nerve damage.

Agricultural use of lepidopteran insecticides dominated insecticide use in this study, and the majority of lepidopteran insecticides were chemicals (Table 1). Indeed, chemical lepidopteran insecticides mainly consisted of organophosphorous, nereistoxin and pyrethroid insecticides with diffferent health toxicities. The increased ALT, GLU and CRP associated with the use of chemical lepidopteran insecticides demonstrated that substantial use of chemical lepidopteran insecticides was likely to damage hepatic function, increase the serum glucose and induce the inflammation among farmers. The consistent results could also be found in the previous studies51,52,53. For example, organophosphorous insecticides against lepidopteran insects were often associated with sub-clinical hepatotoxicity indicated by the increased serum concentrations of ALT in pregnant women and rats51,52. In addition, it was well documented that the majority of organophosphorous, nereistoxin and pyrethroid insecticides against lepidopteran insects were nerve agents34,35,36,37,38,39,40. Our results showed that the potential damage effects of chemical lepidopteran insecticides on the median and ulnar nerves were far severer.

In contrast with chemical lepidopteran insecticides, biological insecticides against lepidopteran insects were not associated with farmer health risk, which was to be expected. The commonly used biological insecticides against lepidopteran insects in China include Bacillus thuringiensis and Helicoverpa armigera nuclear polyhedrosis virus. Although these biological lepidopteran insecticides were increasingly used in China due to their high efficiency and low toxicity in crop protection in recent years, the proportion of these insecticides in the total use of lepidopteran insecticides was only about 11.8% (Table 1). In addition, the insecticides used to control non-lepidopteran insects were also not observed to induce adverse effects on farmer health, which could be attributed to that the relative small amount of these insecticides used by farmers was not enough to induce health risk.

Fungicide use accounted for only 15% of the total use of pesticides (Table 1), less than that of insecticides and herbicides. Anyway, we found that fungicide use was likely to damage hepatic function among farmers. Moreover, fungicide use was also associated with the loss of vitamin B 12 . Note that the most common used fungicides in this study consisted of organosulfur chemicals, mainly including ethylenebisdithiocarbamates (EBDCs) and dimethyldithiocarbamates (DMDCs). In detail, among EBDCs were mancozeb, zineb and metiram, and among DMDCs were thiram and ziram. It was previously documented that these organosulfur fungicides were closely associated with the increases in ALT and AST in humans and animals, which indicated damages to hepatic function54,55,56.

It is notable that agricultural uses of glyphosate, non-glyphosate herbicides and lepidopteran insecticides may be greatly altered if GM glyphosate-tolerant and insect-resistant crops are adopted18,19,20,21,22,23,24. Although the related increase in glyphosate use has raised several concerns on the health and environmental risks18,20, substantial studies indicated that glyphosate may be the least toxic pesticide57,58,59,60. It implies that the adoption of GM glyphosate-tolerant crops may indeed benefit farmer health by sharply reducing the use of the more toxic non-glyphosate herbicides. In addition, it has also been well-documented that GM insect-resistant crops may enable farmers to protect crops more effectively and thus reduce the use of lepidopteran insecticides, especially chemical ones21,22,23,24. In this context, if GM insect-resistant crops are adopted, the alterations in insecticide use may also benefit farmer health by lowering the insecticide exposure level27,61.

Since 46.9% and 42.4% of farmers in our sample had the habits of cigarette intake and alcohol consumption, respectively, we also conducted statistical tests of the different effects between a group of neither cigarette intake nor alcohol consumption and the other three groups (cigarette intake but not alcohol consumption; alcohol consumption but not cigarette intake; and both cigarette intake and alcohol consumption). However, we did not find evidence that the habits of cigarette intake and alcohol consumption aggravated pesticide intoxication in our sample. This result is not surprising because our study focuses on the sub-clinical health effect rather than acute pesticide intoxication or pesticide intake.

There were also some limitations to be pointed out. The relatively small effective sample size and short study period were likely to produce biased results. In addition, although this study examined a wide range of indicators of the blood chemistry panel and peripheral nerve conduction, it was still hardly reflected the complete health status of those farmers, which then called for further related studies in the future.

In conclusion, glyphosate was likely to be the least toxic to farmer health, while non-glyphosate herbicides inclined to induce hazard effect on farmer renal function and serum folic acid. In terms of insecticides, chemicals used to control lepidopteran insects might cause severe health problems, especially the damages to farmer peripheral nerves, while neither biological lepidopteran nor non-lepidopteran insecticides uses were associated with farmer health. Given the findings on the impacts of GM crops on pesticide use and the results about the health effects of the uses of different pesticides related to GM crops in this study, it can be concluded that the alterations in agricultural pesticide use are likely to benefit the health of a large number of farmers in China and even globe if GM crops are adopted. Hence, this study could have positive implications for the development of GM crops.