Pre-emergence herbicides widely used in urban and farmland soils: fate, and potential human and environmental health risks

Abstract

We determined the distribution, fate, and health hazards of dimethenamid-P, metazachlor, and pyroxasulfone, the effective pre-emergence herbicides widely used both in urban and agricultural settings globally. The rate-determining phase of sorption kinetics of these herbicides in five soils followed a pseudo-second-order model. Freundlich isotherm model indicated that the herbicides primarily partition into heterogeneous surface sites on clay minerals and organic matter (OM) and diffuse into soil micropores. Principal component analysis revealed that soil OM (R², 0.47), sand (R², 0.56), and Al oxides (R², 0.33) positively correlated with the herbicide distribution coefficient (K_d), whereas clay (R², ‒ 0.43), silt (R², ‒ 0.51), Fe oxides (R², ‒ 0.02), alkaline pH (R², ‒ 0.57), and EC (R², ‒ 0.03) showed a negative correlation with the K_d values. Decomposed OM rich in C=O and C-H functional groups enhanced herbicide sorption, while undecomposed/partially-decomposed OM facilitated desorption process. Also, the absence of hysteresis (H, 0.27‒0.88) indicated the enhanced propensity of herbicide desorption in soils. Leachability index (LIX, < 0.02-0.64) and groundwater ubiquity score (GUS, 0.02‒3.59) for the soils suggested low to moderate leaching potential of the herbicides to waterbodies, indicating their impact on water quality, nontarget organisms, and food safety. Hazard quotient and hazard index data for human adults and adolescents suggested that exposure to soils contaminated with herbicides via dermal contact, ingestion, and inhalation poses minimal to no non-carcinogenic risks. These insights can assist farmers in judicious use of herbicides and help the concerned regulatory authorities in monitoring the safety of human and environmental health.

Keywords: Ecological risks; Leaching potential; Nontarget biota; Sorption‒desorption; Urban and agricultural settings; Weedicides.

Fig. 1

Fourier-transform infrared (FTIR) spectra representing the functional groups of organic matter present in urban soils CAL and FLE, and agricultural soils QLD, MAT, and TAR

Fig. 2

SEM image of agricultural soils a QLD, b MAT, and c TAR. Urban soils d CAL and e FLE showing undecomposed and partially decomposed OM

Fig. 3

SEM–EDS of the corresponding C-loaded OM in urban soils a CAL, and b FLE, highlighting C on per cent weight basis, and their relative molecular positions (right panels)

Fig. 4

Equilibrium curves a, b, c, and Freundlich isotherms d, e, f of dimethenamid-P, metazachlor, and pyroxasulfone sorption in urban soils CAL and FLE, and agricultural soils QLD, MAT, and TAR. Q_t (mg/kg) is the amount of sorbed herbicide at time ‘t’; C_e (mg/L) is the equilibrium concentration and Q_e (mg/kg) is the equilibrium sorbed concentration of the herbicide

Fig. 5

Equilibrium curves a, b, c, and Freundlich isotherms d, e, f of dimethenamid-P, metazachlor, and pyroxasulfone desorption in urban soils CAL and FLE, and agricultural soils QLD, MAT, and TAR. Q_t (mg/kg) is the amount of sorbed herbicide at time ‘t’; C_e (mg/L) is the equilibrium desorbed concentration and Q_e (mg/kg) is the equilibrium sorbed concentrations of the herbicide after one desorption cycle

Fig. 6

PCA score plots for dimethenamid-P, metazachlor, and pyroxasulfone sorption distribution coefficient (K_d) in urban soils CAL and FLE, and agricultural soils QLD, MAT, and TAR

Fig. 7

Potential non-cancer health risk in terms of hazard index (HI) for human adults and adolescents exposed to urban soils CAL and FLE, and agricultural soils QLD, MAT, and TAR contaminated with dimethenamid-P, metazachlor, and pyroxasulfone