Occurrence and determination of herbicides and their major transformation products in environmental waters

Abstract

A method for the simultaneous determination of selected maize and grain herbicides (amidosulfuron, N-([{[(4,6-dimethoxy-2-pyrimidinyl)amino]carbonyl}amino)sulfonyl]- N-methylmethanesulfonamide; bentazone, 3-(1-methylethyl)-1H-2,1,3-benzothiadiazin-4(3H)-one2,2-dioxide; 2,4-D, (2,4-dichlorophenoxy)acetic acid; MCPA, (4-chloro-2-methylphenoxy)acetic acid; metosulam, N-(2,6′-dichloro-3-methylphenyl)-5,7-dimethoxy[1,2,4]triazolo[1,5- a]pyrimidine-2-sulfonamide) and their transformation products (TPs) (8-hydroxybentazone, 1H-2,1,3-benzothiadiazin-4(3H)-one,8-hydroxy-3-(1-methylethyl)-2,2-dioxide; bifenox acid, 5-(2,4-dichlorophenoxy)-2-nitrobenzoic acid; clodinafop acid; 2,4-dichlorophenol; 4-chloro-2-methylphenol) in environmental waters was developed. The procedure combines a solid-phase extraction (SPE) with column liquid chromatography–tandem mass spectrometry detection utilizing a pneumatically assisted and heat-assisted electrospray interface in negative mode. The extraction of analytes from filtered drainage or river water samples was performed using as sorbent a graphitized carbon. The recovery, for drinking water, ranged from 91 to 98%, and from 84 to 95% for river water. Excellent method precision was demonstrated with percent relative standard deviation of less than 10% for all analytes at fortification level. Detection limits were at level of few nanograms per liter, except for 2,4-dichlorophenol and 4-chloro-2-methylphenol, that was in the range of tens of nanogram per liter. The present methodology was used for searching in river and drainage waters of maize-grain fields of the Tiber valley, during a typical period of herbicides application from April to July 2001. The levels detected of four compounds were in the range of: non-detectable (ND)–6.1, ND–27, ND–1.9 and ND–0.5 μg l −1, for MCPA, bentazone, 8-hydroxybentazone and 2,4-D, respectively. Detectable amounts of bentazone-8-hydroxy at level of 0,3 μg l −1 was found to be transported into river. The highly satisfactory results for all target analytes demonstrate the potential of liquid chromatography–tandem mass spectrometry for the identification and the quantification of the polar and acidic herbicides at below 100 ng l −1 levels.