Toxicity of formulants and heavy metals in glyphosate-based herbicides and other pesticides

Abstract

The major pesticides of the world are glyphosate-based herbicides (GBH), and their toxicity is highly debated. To understand their mode of action, the comparative herbicidal and toxicological effects of glyphosate (G) alone and 14 of its formulations were studied in this work, as a model for pesticides. GBH are mixtures of water, with commonly 36-48% G claimed as the active principle. As with other pesticides, 10-20% of GBH consist of chemical formulants. We previously identified these by mass spectrometry and found them to be mainly families of petroleum-based oxidized molecules, such as POEA, and other contaminants. We exposed plants and human cells to the components of formulations, both mixed and separately, and measured toxicity and human cellular endocrine disruption below the direct toxicity experimentally measured threshold. G was only slightly toxic on plants at the recommended dilutions in agriculture, in contrast with the general belief. In the short term, the strong herbicidal and toxic properties of its formulations were exerted by the POEA formulant family alone. The toxic effects and endocrine disrupting properties of the formulations were mostly due to the formulants and not to G. In this work, we also identified by mass spectrometry the heavy metals arsenic, chromium, cobalt, lead and nickel, which are known to be toxic and endocrine disruptors, as contaminants in 22 pesticides, including 11 G-based ones. This could also explain some of the adverse effects of the pesticides. In in vivo chronic regulatory experiments that are used to establish the acceptable daily intakes of pesticides, G or other declared active ingredients in pesticides are assessed alone, without the formulants. Considering these new data, this assessment method appears insufficient to ensure safety. These results, taken together, shed a new light on the toxicity of these major herbicides and of pesticides in general.

Keywords: Arsenic; Formulant; G, glyphosate; GBH, glyphosate-based herbicide; Glyphosate; Heavy metals; Herbicide; POEA; POEA, polyoxyethylenamines (polyethoxylated tallowamine); Pesticide; QAC, quaternary ammonium compounds; R, Roundup; Roundup.

Graphical abstract

Fig. 1

Glyphosate (G) alone does not demonstrate herbicidal activity. Tomato plants were watered and sprayed during 120 h with 80 mL/day of water only (control C), or G alone at the same concentration as in the G-based herbicide R1 (Glyphogan) used at the recommended agricultural dilution of 11.25 mL/L (1.1%), like R2 (Roundup GT+) and R3 (Roundup WeatherMax). The main family of formulants (F, Genamin, 70% POEA) of R1 alone exerted the herbicidal action at the concentration present in R1. This was reproduced 3 times and outdoors, and in field also on a square meter of grass. After one week, the results were similar than after 120 h.

Fig. 2

Human embryonic cells are killed by glyphosate-based formulations (GBH) and the formulant family, but not by G. The treatments for HEK293 cells over 90 min are like those of Fig. 1; chemicals are diluted in cell medium EMEM in quantities equivalent to the recommended agricultural use of 1.1% for R1.

Fig. 3

Comparative cytotoxicities of 14 glyphosate-based herbicide (GBH) formulations, 5 formulants and G alone or its salt. Effects on mitochondrial succinate dehydrogenase (SD) activity, reflecting cell respiration inhibition, were measured in HEK293 human cells after 24 h exposure and expressed in ppm¹ (1/LC50). LC50 values were calculated by a nonlinear regression using sigmoid (5-parameters) equation, SEM are indicated. Control is at 0. Formulants are in grey, formulations in black and isopropylamine salt of G (G IPA) and G alone in white. Genamin consists of 70% POEA.

Fig. 4

Endocrine disruptions occur below observable toxicity. Six representative formulations and 4 formulants (underlined in x axis), and G salt, were studied comparatively for their aromatase inhibition with the first threshold of around 25% (circles) and their lowest observable toxicity (squares), expressed in ppm of each product.

Fig. 5

Heavy metals in formulations of pesticides in comparison to admissible levels in water in the EU [17] (red lines) corresponding to the WHO guideline values [18] (As 10 ppb; Cr 50 ppb; Ni; Pb 10 ppb) except of Ni (20 ppb vs 70 ppb respectively); no existing value for Co (48).

Fig. 6

Heavy metals in formulations of pesticides at their recommended dilutions.