Volatilization of Alachlor and Atrazine as Influenced by Surface Litter

A basic knowledge of how herbicide volatilization is influenced by agronomic practices is necessary if long-term detrimental impacts from herbicides are to be minimized. We measured cumulative herbicide volatilization losses in glass agroecosystem chambers to assess how surface residue conditions, simulated rainfall, temperature, and herbicide formulation affect volatilization of atrazine and alaehlor. Research results demonstrated that herbicide volatilization before water application was greater under mulched conditions, but decreased dramatically after the first irrigation. As a result, after 35 d cumulative volatilization of atrazine from a mulched soil surface was less than half that from bare soil for both formulations. Plant litter on the soft surface and encapsulated herbicides may be viable alternatives for reducing volatilization of some herbicides in humid regions

L Band Brightness Temperature Observations Over a Corn Canopy During the Entire Growth Cycle

During a field campaign covering the 2002 corn growing season, a dual polarized tower mounted L-band (1.4 GHz) radiometer (LRAD) provided brightness temperature (T(sub B)) measurements at preset intervals, incidence and azimuth angles. These radiometer measurements were supported by an extensive characterization of land surface variables including soil moisture, soil temperature, vegetation biomass, and surface roughness. During the period from May 22, 2002 to August 30, 2002 a range of vegetation water content (W) of 0.0 to 4.3 kg/square m, ten days of radiometer and ground measurements were available. Using this data set, the effects of corn vegetation on surface emissions are investigated by means of a semi-empirical radiative transfer model. Additionally, the impact of roughness on the surface emission is quantified using T(sub B) measurements over bare soil conditions. Subsequently, the estimated roughness parameters, ground measurements and horizontally (H)-polarized T(sub B) are employed to invert the H-polarized transmissivity (gamma-h) for the monitored corn growing season

Prevalence of hepatic iron overload and association with hepatocellular cancer in end-stage liver disease: results from the National Hemochromatosis Transplant Registry

Background : It is unclear whether mild to moderate iron overload in liver diseases other than hereditary haemochromatosis (HH) contributes to hepatocellular carcinoma. This study examined the association between hepatic iron grade and hepatocellular carcinoma in patients with end-stage liver disease of diverse aetiologies. Methods : The prevalence of hepatic iron overload and hepatocellular carcinoma was examined in 5224 patients undergoing liver transplantation. Explant pathology reports were reviewed for the underlying pathological diagnosis, presence of hepatocellular carcinoma and degree of iron staining. The distribution of categorical variables was studied using Χ 2 tests. Results : Both iron overload and hepatocellular carcinoma were the least common with biliary cirrhosis (1.8 and 2.8% respectively). Hepatocellular carcinoma was the most common in patients with hepatitis B (16.7%), followed by those with hepatitis C (15.1%) and HH (14.9%). In the overall cohort, any iron overload was significantly associated with hepatocellular carcinoma ( P =0.001), even after adjustment for the underlying aetiology of liver disease. The association between hepatic iron content and hepatocellular carcinoma was the strongest in patients with biliary cirrhosis ( P <0.001) and hepatitis C ( P <0.001). Conclusions : Iron overload is associated with hepatocellular carcinoma in patients with end-stage liver disease, suggesting a possible carcinogenic or cocarcinogenic role for iron in chronic liver disease.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/75573/1/j.1478-3231.2007.01596.x.pd

L Band Brightness Temperature Observations over a Corn Canopy during the Entire Growth Cycle

During a field campaign covering the 2002 corn growing season, a dual polarized tower mounted L-band (1.4 GHz) radiometer (LRAD) provided brightness temperature (TB) measurements at preset intervals, incidence and azimuth angles. These radiometer measurements were supported by an extensive characterization of land surface variables including soil moisture, soil temperature, vegetation biomass, and surface roughness. In the period May 22 to August 30, ten days of radiometer and ground measurements are available for a corn canopy with a vegetation water content (W) range of 0.0 to 4.3 kg m−2. Using this data set, the effects of corn vegetation on surface emissions are investigated by means of a semi-empirical radiative transfer model. Additionally, the impact of roughness on the surface emission is quantified using TB measurements over bare soil conditions. Subsequently, the estimated roughness parameters, ground measurements and horizontally (H)-polarized TB are employed to invert the H-polarized transmissivity (γh) for the monitored corn growing season

Effect of Formulation and Tillage Practice on Volatilization of Atrazine and Alachlor

Conservation tillage practices are being implemented by many farmers to conserve water and soil resources. These practices may modify the soil surface in ways that differentially effect dissipation of pesticide when compared to conventionally tilled fields. We measured volatilization of atrazine [2-chloro-4-ethylamino-6-isopropylamino-s-triazine] and alachlor [2-chloro-2\u27-6\u27-diethyl-n-(methoxymethyl) acetanilide] applied as either an experimental starch-encapsulated formulation or as a commercial formulation, containing atrazine as a wet table powder and microencapsulated alachlor, to adjacent no-till and conventionally tilled corn fields in Maryland. Both formulations were applied at the same rate; 1.7 kg ha‒1 for atrazine and 2.8 kg ha‒1 for alachlor. After 35 d, cumulative volatilization of alachlor from conventionally tilled fields was 14% of that applied for both formulations. Cumulative volatilization of alachlor was less from no-till fields with 9% of the commercial formulation and 4% of the starch-encapsulated formulation being lost. After 35 d, cumulative volatilization of the commercial formulation of atrazine from the conventionally tilled field was 9% of that applied compared with 4% of that applied to the no-till field. Starch encapsulation reduced volatilization losses of atrazine t

Effect of Water Potential, Temperature, and Soil Microbial Activity on Release of Starch-Encapsulated Atrazine and Alachior

Starch encapsulation has been proposed as a method for controlling the rate at which pesticides are released into the soil. Relatively little is known about what environmental factors influence controlled release. A series of laboratory studies were initiated to improve our understanding of how water potential, temperature, and soil microbial activity influence rate of release of starch-encapsulated atrazine (2-chloro-4ethylamino-6-isopropylamino-s-triazine) and alachlor (2-chloro-2’,6’-diethyl-N-(methoxymethyl)-acetanilide). Water potential, imposed using polyethylene glycol, significantly influenced swelling of the starch matrix and rate of release of both herbicides. At a water potential of 0 MPa, complete release required 21 d for atrazine and 7 d for alachlor. As water potential declined, so did rate of release. At a water potential of ‒1.5MPa, less than 50% of the encapsulated atrazine and less than 80% of the encapsulated alachlor had diffused out of the starch matrix after 28 d temperature also influenced rate of release of both herbicides. At 35°C nearly three times more atrazine and two times more alachlor was released from starch granules than at 15°C at all sampling times. Soil microbes increase the rate of release. After 21 d there was a twofold increase in the percentage of atrazine released from starch granules applied to sterile soil. Effect of soil microbes on rate of alachlor release was apparent only at early times. After 5 d there was a 20% increase in the percentage of alachlor released from starch granules when microbes were present compared with release from starch granules applied to sterile soil. After 14 d essentially all of the alachlor had been released from starch granules applied to either sterile or nonsterile soil. The difference influences that water potential, temperature, and soil microbes have on rate of release between atrazine and alachlor are likely due to differences in water solubility of atrazine (30 mg L-1) and alachlor (240 mg L-1

Effect of Starch Encapsulation and Temperature on Volatilization of Atrazine and Alachlor

Volatilization of agricultural chemicals is one process whereby chemicals may enter into parts of the environment where they were not intended. Starch encapsulation of pesticides has been proposed as a way of modifying pesticide behavior in the soil environment. This study was conducted to assess how starch encapsulation and temperature affect volatilization of atrazine [6-chloro-N-ethyI-N’-(1-methylethyl) - 1, 3, 5-triazine-2,4-diamine] and alachlor [2-chloro-N-(2,6- diethylphenyl)-N-(methoxymethyl)acetamide]. Volatilization measured using agroecosystem chambers as model systems. Herbicides were applied at rates of 1.7 kg ha‒1 -for atrazine and 2.8 kg ha‒1 for alachlor, as either a commercial formulation or a starch encapsulated formulation, to the surface of moist soils maintained at temperatures of 15, 25 and 35°C. Air was drawn through the chambers (2.5 m3 min‒1) and herbicide in the vapor phase was t rapped in polyurethane foam plugs. Volatilization of both herbicides increased as temperature increased. Volatilization of atrazine was less when applied as starch encapsulated formulation than the commercial formulation. After 35 d cumulative volatilization of atrazine ranged from \u3c 1% of that applied as starch-encapsulated formulation at 15 °C, to 14% of that applied as the commercial formulation at 35 °C. Cumulative volatilization of alachlor was greater when applied as starch-encapsulated formulation than as the commercial formulation. After 35 d, cumulative volatilization of alachlor ranged from \u3e 2% of that applied as either formulation at 15 °C to 32% of that applied as starch encapsulated formulation at 35 °C. Differences in volatilization behavior between these herbicides are likely to be due to differences in chemical properties of these herbicides

Herbicide Leaching under Tilled and No-Tillage Fields

The effect of no-tillage practices on water quality exiting the root zone of deep, well-drained fields is largely unknown. This project was initiated to determine herbicide leaching characteristics as influenced by tillage practice and herbicide formulation. The research site consisted of four adjacent (0.25-ha) fields, two fields each dedicated to either tilled or no-tillage management. One field in each tillage regime received a controlled-release formulation of atrazine [6-chloro-N-ethyl- N\u27-(1-methylethyl)-1,3,5-triazine-2,4-diamine] and alachlor [2-chloro- N-(2,6-diethylphenyl)-N-(methoxymethyl)-acetamide, starch encapsulated], while the others received standard herbicide formulations of atrazine and alachlor. Both herbicide formulations were annually applied at the same rate: 1.7 kg ha‒1 for atrazine and 2.8 kg ha‒1 for alachlor. Atrazine, deethylatrazine [DEAT; 6-chloro-N-(l-methylethyl)- 1,3,5-triazine-2,4-diamine], alachlor, and Br ‒ concentrations were monitored with 12 suction lysimeters (six each at 1.5- and 1.8-m depths) in each field. Alachlor was detected in \u3c3% of all samples collected, regardless of tillage practice or herbicide formulation, while atrazine was detected in \u3e41% of the samples. Under no-tillage, atrazine was detected in \u3c28% of the samples with \u3c13% exceeding the U.S. Environmental Protection Agency Health Advisory level of 3 μg L‒1 atrazine. Under tilled conditions, 53% of the samples contained atrazine, with 35% exceeding 3 μg L‒1 atrazine. Averaged atrazine metabolite concentration of DEAT under no-tillage was 0.52 μg L‒1 vs. 0.39 μg L‒1 for tilled fields. Similar Br ‒ transport between tillage practices and reduced atrazine levels under no-tillage fields suggest that no-tillage management, on deep well-drained soils, can have a positive impact on groundwater quality