The uptake by roots from solution, and subsequent translocation to shoots in barley, of two series of non-ionised chemicals, O-methylcarbamoyloximes and substituted phenylureas, were measured, Uptake of the chemicals by roots was greater the more lipophilic the chemical, and fell to a lower limiting value for polar chemicals. Translocation to the shoots was a passive process, and was most efficient for compounds of intermediate polarity. Both processes had reached equilibrium within 24h of treatment. The reported behaviour of many pesticides in various plant species agrees with the derived relationships, but the detailed mechanisms of these processes are unknown.

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Relationships between lipophilicity and root uptake and translocation of non-ionised chemicals by barley†

Uptake and transport mechanisms of decabromodiphenyl ether (BDE-209) by rice (Oryza sativa).

Soil columns were used to investigate leaching of atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine] in a Plainfield sandy soil amended with waste activated carbon (WAC), digested municipal sewage sludge (DMS), or animal manure. Lower amounts of atrazine were consistently observed in leachates from soil with amendments than from soil without amendments. Ability of the three wastes to reduce leaching of atrazine followed the order WAC ≫ DMS > animal manure. Atrazine recovery in leachate ranged from 0.1% from soil amended with WAC at 2.1 t of total carbon per ha (t C/ha) to 77.4% from unamended soil. Mobility of atrazine in amended soil was inversely related to its sorption coefficient, KOC. Reduction in amount of leached atrazine by application of DMS or manure may also have involved increased degradation and/or formation of bound residues. Findings of this study provide basic information for possible utilization of waste materials in coarse-textured soils to reduce leaching of pesticides to ground water.

Effect of carbon-rich waste materials on movement and sorption of atrazine in a sandy, coarse-textured soil

Groundwater (GW) constitutes the most important source of drinking water, and despite the benefit of pesticides in food production, the contamination of GW by biologically active pesticides at unacceptable levels should be avoided. A number of pesticides and their degradation products have frequently been detected in field GW monitoring programs (Cohen et al. 1984; Hancock et al. 2008; Kolpin et al. 2000). Regulatory agencies in each country are responsible for preventing contamination of GW by pesticides or their degradates. Regulators have developed methods to assess both existing and newly developed pesticides for any tendency to leach in soil. The US EPA has performed monitoring studies to determine if pesticides contaminate GW (Wells et al. 1995) and has recently introduced a conceptual environmental model to better evaluate GW contamination (USEPA 2008b). In Europe, a stepwise evaluation procedure for regulating GW contamination by pesticides and their degradates is used, and this has recently been updated; the revision not only utilizes computer simulations of predicted environmental concentrations to determine if the 0.1 ppb trigger level is exceeded, but also relies on data from higher-tier field experiments (Boesten et al. 2009). To estimate the leaching behavior of a pesticide in soil or to compare its relative mobility with other pesticides, the sophisticated simulation approaches used generally require considerable data on the environmental fate of the pesticide. Because the cost of conducting field experiments over extended time periods can be extremely high, it is useful to collect relevant information on pesticide soil mobility by first using experimental laboratory approaches. For soil mobility, such approaches include batch adsorption studies, soil thin-layer chromatography, and soil column leaching (Hafner 1994; Helling and Dragun 1981; USEPA 2008a). Although laboratory soil column leaching and batch adsorption/desorption studies have been performed on many pesticides, the results of these studies do not always reflect what actually occurs in the field. Nevertheless, such studies normally provide valuable information on the potential mobility of pesticides in soil if they are well-controlled and focused, and the results are mathematically analyzed using an appropriate model.

Soil column leaching of pesticides.

This work describes the accumulation and dis- tribution of the herbicide atrazine in soil, water, and roots from three wetland model systems using the monocots Typha domingensis, Sagittaria lancifolia, and Echinochloa pyra- midalis. Results were analyzed from a 3 3 full factorial experimental design, in order to describe the effect of accumulation of atrazine and times of exposure in the species evaluated. We found that accumulation depends on the species and the herbicide concentration; about 30% was accumulated in soil, 40% in roots, and 10-20% in water. By the end of the experiment, E. pyramidalis accumulated 8.47 mg/l of atrazine and 14.39 mg/l T. domingensis; in all cases, adsorption accounted for 1.4%, fitting a Langmuir model with a kd of 14.47.

Short-term accumulation of atrazine by three plants from a wetland model system.

The uptake of five herbicides by the dead roots of six plant species was investigated and it is concluded that the process involved was probably adsorption The adsorptive capacity of the dry matter of roots was lower than soil organic matter but was of a similar order of magnitude It is suggested that in some cases adsorption might provide a significant pathway by which herbicides are taken up by the living plant It seems unlikely that adsorption by roots will normally exert much influence on the herbicide concentration in the soil solution

R. S. Tames

Papers

The adsorption of herbicides by roots