Weed detection

Atrazine, used as a selective pre- and post-emergence herbicide to control annual weeds in several crops, is the most representative compound of this group. It is also used as a non-selective herbicide in non-crop areas. After absorption, the compound is metabolized to dealkylated and deisopropy-lated derivatives. The unchanged compound and its metabolites are excreted in urine, where they can be detected by chromatography or enzyme-linked immunosorbent assay (Lucas et al., 1993). A mercapturic acid conjugate of atrazine has also been found in urine samples of workers spraying this herbicide (Lucas et al., 1993) (Table 6). 

Compared to the preventative strategies described above, weed control is thought to have a relatively minor effect on Fusarium infection and mycotoxin levels in grain, but there are few studies available. However, it should be noted that weed density is often higher in organic farming systems and that certain weeds can act as alternative hosts for Fusarium. For example, Fusarium contamination has been detected by Meier (2003) especially on climbing... 

Acrolein enters the environment as a result of normal metabolic processes incomplete combustion of coal, wood, plastics, tobacco, and oil fuels and industrial emissions. Acrolein has been detected in smog, foods, and water. It is used extensively in chemical manufacture, for control of fouling organisms, and as an herbicide to control submerged weeds in irrigation canals. 

Paraquat is used to control aquatic weeds. It also passes into aquatic environments through rain, where it is rapidly accumulated by aquatic organisms, especially fish (Gabryelak and Klekot 1985). Paraquat applied to control aquatic weeds is accumulated by aquatic macrophytes and algae, and it is adsorbed to sediments and suspended materials. Initial applications of 1 to 5 mg/L in the water column are usually not detectable under field conditions after 8 to 27 days (Summers 1980). The half-time persistence of paraquat in water column at normal doses for weed control (i.e., 0.5 to 1.0 mg/L) was 36 h less than 0.01 mg/L was detectable in 2 weeks (Calderbank 1975). In solution, paraquat was subject to photodecomposition and microbial metabolism, degrading to methylamine... 

Allelopathy found hopeful utilization in plant protection against parasite weeds. The main world parasitic species are the witchweeds (Striga spp.), broomrapes (Orobanche spp.), and eventually dodder (Cuscuta spp.). Witchweeds and broom-rapes attack many economically important crops especially throughout the semi-arid regions. Early detection of parasitic weed infestation and protection is difficult because of the growth habit of a root parasite and huge production of dust-like seeds viable up to 20 years (Kebreab and Murdoch 1999). 

Biological chemical detection, chemical sensors versus, 22 269 Biological Control of Weeds Handbook,... 

Following an aviation kerosin spill, hydrocarbons were detected in trout stream sediments and fish up to 14 months after the spill [13]. After a fire at a weed treatment plant in 1970 a large area of mixed forested ecosystem became contaminated with polycyclic aromatic hydrocarbons and creosote [66], High polyaromatic concentrations in stream sediments adversely affected micro- and meiobenthic communities at all trophic levels. Stein et al. [67] have studied the uptake by bethnic fish (English sole, Parophrys vetulus) of benzopyrene and polychlorinated biphenyls from sediments. Accumulation of contaminants from sediments was a significant route of uptake by English sole. 

Dacthal is a widely used pre-emergent herbicide that is applied to many crops for the control of annual weeds. Dacthal is typically applied to agricultural soils at 6-14kg ha [214], In the soil environment, Dacthal transforms to mono- and diacid-metabolites that are more water soluble than the parent herbicide [215-217]. In eastern Oregon, where Dacthal is applied to onions, the diacid metabolite is the principal form of Dacthal detected in groundwater obtained from domestic wells [218, 219],... 

Since the last part of the 20th Century, the issue of pesticides in foods has generated considerable public concern and debate. Pesticides are chemicals designed specifically for their toxicological effects on target pests, such as insects, weeds, and plant diseases. Public awareness that such chemicals are commonly detected in the food supply as residues contributes greatly to the debate. 

Most of the compounds of arsenic are toxic when in contact with the skin, when inhaled, or when ingested. As with arsenics cousin phosphorus above it in group 15 of the periodic table, care must be taken when using arsenic. The compound arsenic trioxide (As O ), an excellent weed-killer, is also carcinogenic. Copper acetoarsenite, known as Paris green, is used to spray cotton for boll weevils. A poisonous dose of arsenic as small as 60 miUigrams can be detected within the body by using the Marsh test. 

In 1909—10 Professor E. H. S. Bailey and Dean L. E. Sayre of the University of Kansas detected barium in the ash and extract of elder, ragweed, agrimony, and certain other Kansas weeds (107, 108). It is also present in minute amounts in many edible plants (107). 

Carbamates and substituted ureas are a numerous group of pesticides widely used to control weeds, pests, and diseases in fruit trees, vegetables, and cereals. Carbamate residues in foods are commonly extracted with water-miscible solvents and determined by using a liquid chromatograph equipped with a sensitive detector, frequently a UV detector. In addition, to obtain adequate detection selectivity, the postcolumn fluorimetric labeling technique is used for methyl carbamates. Substituted ureas are normally extracted from foods with organic solvents, and they can be determined directly by HPLC-UV or after postcolumn derivatization by fluorescence determination of their derivatives. 

Dicamba was not detected in Lake Superior in 1996 and 1997. Its concentration in each of the lakes decreased in the order Lake Huron/Georgian Bay > Erie > Ontario > Superior. Dicamba, like 2,4-D, may also be applied in urban areas several times from spring through fall for broadleaf weed control. 

Chlorophenoxy acid herbicides are also widely used to control broadleaf weeds and grass plants. Several immunoassays have been reported for 2,4-dichlorophenoxyacetic acid (2,4-D) and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T).246 247 Several immunosensors have been described using a transducing principle similar to the RIANA system already described in this chapter. Thus, Meusel et al.248 reported the use of monoclonal antibodies in a sensor chip to analyze river and lake water samples, obtaining detection limits of 0.1 ig L 1. Moreover, monoclonal antibodies, produced by Cuong et al.,249 were used in a dipstick immunoassay format to analyze pond water samples. When applied to the 2,4-D compound, this semiquantitative method yielded for an IC50 of 6 ug I. and an LOD of 0.5 pg L-1. 

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