Alachlor distribution

Results of adsorption experiments for butylate, alachlor, and metolachlor in Keeton soil at 10, 19, and 30°C were plotted using the Freundlich equation. A summary of the coefficients obtained from the Freundlich equation for these experiments is presented in TABLE IV. Excellent correlation using the Freundlich equation over the concentration ranges studied (four orders of magnitude) is indicated by the r values of 0.99. The n exponent from the Freundlich equation indicates the extent of linearity of the adsorption isotherm in the concentration range studied. If n = 1 then adsorption is constant at all concentrations studied (the adsorption isotherm is linear) and K is equivalent to the distribution coefficient between the soil and water (Kd), which is the ratio of the soil concentration (mole/kg) to the solution concentration (mole/L). A value of n > 1 indicates that as the solution concentration increases the sorption sites become saturated, resulting in a disproportionate amount of chemical being dissolved. Since n is nearly equal to 1 in these studies, the adsorption isotherms are nearly linear and the values for Kd (shown in TABLE IV) correspond closely to K. These Kd values were used to calculate heats of adsorption (AH). 

Heats of Adsorption. Temperature effects were determined by measuring adsorption at three temperatures. As seen from TABLE IV, the K values vary with temperature such that for butylate, K increases with temperature, while for alachlor and metolachlor, K decreases with temperature. These results indicate that butylate becomes more adsorbed to Keeton soil as the temperature increases while alachlor and metolachlor become less adsorbed as temperature increases. In order to obtain a quantitative measure of these effects, heats of adsorption (AH) were calculated as described previously in the Materials and Methods section (equation 3). TABLE IV contains values for the average molar distribution constants (Kd) for butylate, alachlor, and metolachlor which were plotted vs the inverse temperatures (1/°K) to obtain the AH s shown in Figure 3. 

Soil Column Leaching. The distribution of radioactivity from [ 1 C]butylate applied at 4.5 KG/HA and [1 l C]alachlor and [1 C] — metolachlor applied at 2.25 KG/HA and leached with 15 cm of water in Felton sand, is shown in Figure 4. Although all three herbicides are mobile in this soil type, butylate showed less mobility, with 59.6% of the applied raidoactivity found in the upper 10 cm of the column, while 28.4% and 24.3% of the applied 1 C was found in the upper 10 cm of the alachlor and metolachlor columns, respectively. 

Among all the compounds analyzed, only eight (OP, NP, TBP, BPA, diazinon, propanil, alachlor and molinate) appeared in both matrices. The most noticeable fact is that NP is the compound that contributes more than the other compounds in both water and sediments, as it has medium value for log K0w (4.48) and the concentrations found were high enough to enable its distribution between the two matrices, between 69 and 5,999 pg kg 1 in the solid matrix. These high concentrations in the sediments are in the same range as in other rivers of the world. This compound shows a lower importance in the PCA analysis because of its appearance as punctual pollutant, mainly around the industrial area of Zaragoza. The rest of the profile shows some differences between water and sediments. Water moves constantly while the sediments are more bound to one location, and in consequence, the... 

TABLE 4.6. Freundlich Adsorption Constants (1In and K) and Distribution Coefficients (Kd) for Adsorption of Alachlor (Generally Linear Isotherms), Imazethapyr (Nonlinear Freundlich Isotherms), and Rimsulfuron (Langmuir Isotherms) on Humic Acids (HAs) Isolated from Two Sewage Sludges (SSI and SS2), a Soil Amended with 10tha 1yr 1 of SSI for 2 Years (SOI + SSI), and a Soil Amended with 40(ha 1yr 1 of SS2 for 2 Years (S02 + SS2), with the Corresponding Unamended Soils (SOI and S02, Respectively) (from Senesi et al., 2001)... 

Freundlich adsorption coefficients (K) and distribution coefficients (Kd), which are indexes of the adsorption capacity of the various HAs for the pesticides, are reported in Tables 4.6 and 4.7. Regardless of the nature of the HA, rimsulfuron is adsorbed in amounts about 10 times higher than those of imazethapyr, which in turn is adsorbed in amounts about two times higher than those of alachlor (Table 4.6). Trans- and dx-chlordane are absorbed in amounts more than one order of magnitude than those of triallate (Table 4.7). Furthermore, trans-chlordane appears to be more adsorbed than dx-chlordane by any HA examined. 

Huang, L.Q. and C.R. Frink (1989). Distribution of atrazine, simazine, alachlor, and metolachlor in soil profiles in Connecticut. Bull. Environ. Contam. Toxicol., 43 159-164. 

Size distribution of Chlamydomonas cell cultures treated with alachlor... 

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