Adsorption, Mobility, and Filtration of Metolachlor in Container Media

Abstract

<jats:p>Adsorption, mobility, and filtration ability of organic media toward metolachlor were evaluated in a series of laboratory experiments. Experimental variables included media type, metolachlor concentration, and equilibration time. Adsorption isotherms were determined by applying the log form of the Freundlich equation. Mobility was evaluated using glass columns filled with media, which were then surface spiked with metolachlor and then leached daily for 10 consecutive days. Peat, pine bark, combinations of these two media and a mixture of pine bark and sand adsorbed &gt;90% of the <jats:sup>14</jats:sup>C metolachlor. Freundlich sorption coefficients were 10.9, 18.2, 13.4, 14.2, and 11.0 for pine bark, peat, 5 pine bark: 1 peat, 3 pine bark: 1 peat, and 5 pine bark: 1 sand, respectively. In a timed exposure experiment using bark, minimum metolachlor adsorption (57%) was at 90 seconds and maximum adsorption (82%) required at least 1440 minutes. In column leaching studies, data for all media indicate that metolachlor is relatively immobile through these substrates. An initial pulse of metolachlor (&lt;1.0 μg·liter<jats:sup>-1</jats:sup>) was detected with each medium up to the third wetting event with a subsequent decline (&gt;0.5 μg·liter<jats:sup>-1</jats:sup> for each medium) in the metolachlor recovered. Filtration efficiency of commercially formulated metolachlor from water passed through different lengths of pine bark filled filters was 0%, 17%, 20%, 22%, 23%, and 29% for filters 4, 20, 12, 8, 16, and 24 cm in length, respectively. These results support the contention that such filtration would be effective provided the residence time of water within the filter was sufficient for adsorption of the contaminant by the media to occur.</jats:p>

Timed Release of Flurprimidol from a Granular Formulation in Mulches and Sand

“…Bulk densities were 0.16, 0.17, 1.5 gÁcm -3 for pine bark, hardwood bark, and sand, respectively. The results of analysis were similar to other reports for pine bark (Brown and Pokorny, 1975;Daniels and Wright, 1988;Grey et al, 1996;Simmons and Derr, 2007) and hardwood bark (Brake et al, 1992). The sand was 90% sand, 0% silt, and 10% clay.…”

“…Pine bark, hardwood bark, and sand macropore space were 54%, 65%, and 6%, whereas waterholding capacity was 79%, 134%, and 30%, respectively. Simmons and Derr (2007) reported similar pore space volumes for pine bark and Grey et al (1996) reported similar gravimetric waterholding capacity for pine bark. Hardwood bark was very absorptive to water.…”

Concurrent nitrate and atrazine retention in bioreactors of straw and bark mulch at short hydraulic residence times

“…as a cost-efficient substitute for activated carbon as adsorbent for anthropogenic contaminants, e.g., dye (Leitch et al, 2006), phenol (Vázquez et al, 2007), heavy metal ions (Vázquez et al, 1994) and metolachlor (Grey et al, 1996). Gendrault et al (2005) observed high adsorption of atrazine onto pine bark.…”

Leaching of propiconazole and chlorothalonil during production of pinus sylvestris seedlings in containers

“…The adsorption of fungicides to peat and the degradation decreased the concentration of both fungicides in leachates as time passed. In laboratory experiments, adsorption of herbicides, oxadiazon and metolachlor, was over 90% in peat medium (Wehtje et al 1993, Grey et al 1996.…”

“…Besides the characteristics of the active ingredient, the properties of the growing medium and cultural practices in container production influence the fate of the active ingredient in the nursery environment (Landis et al 1991, Torstensson & Stenstrom 1995. Only a few studies have investigated the leaching of herbicides from media used in container nurseries (Wehtje et al 1993, Mahnken et al 1994, Grey et al 1996, but to the authors' knowledge there are no published results about leaching of pesticides during actual production of container forest seedlings. Therefore, the objective of this study was to determine possible leaching of propiconazole and chlorothalonil from peat growing medium into the ground during commercial production of container-grown Scots pine seedlings.…”