Evaluating phytochemical and microbial contributions to atrazine degradation.

The inclusion of warm-season grasses, such as switchgrass (Panicum virgatum) and eastern gamagrass (EG) (Tripsacum dactyloides), in vegetated buffer strips has been shown to mitigate herbicide contamination in runoff and increase herbicide degradation in soil. The mode of action by which buffer strip rhizospheres enhance herbicide degradation remains unclear, but microorganisms and phytochemicals are believed to facilitate degradation processes. The objectives of this study were to: 1) screen root extracts from seven switchgrass cultivars for the ability to degrade the herbicide atrazine (ATZ) in solution; 2) determine sorption coefficients (Kd) of the ATZ-degrading phytochemical 2-ß-D-glucopyranosyloxy-4-hydroxy-1,4-benzoxazin-3-one (DBG) to soil and Ca-montmorillonite, and investigate if DBG or ATZ sorption alters degradation processes; and 3) quantify ATZ degradation rates and soil microbial response to ATZ application in mesocosms containing soil and select warm-season grasses. Phytochemicals extracted from the roots of switchgrass cultivars degraded 44-85% of ATZ in 16-h laboratory assays, demonstrating that some switchgrass cultivars could rapidly degrade ATZ under laboratory conditions. However, attempts to isolate ATZ-degrading phytochemicals from plant roots were unsuccessful. Sorption studies revealed that DBG was strongly sorbed to soil (Kd = 87.2 L kg-1) and Ca-montmorillonite (Kd = 31.7 L kg-1), and DBG driven hydrolysis of ATZ was entirely inhibited when either ATZ or DBG were sorbed to Ca-montmorillonite. Atrazine degradation rates in mesocosm soils were rapid (t0.5 = 8.2-11.2 d), but not significantly different between soils collected from the two switchgrass cultivar mesocosms, the eastern gamagrass cultivar mesocosm, and the unvegetated mesocosm (control). Significant changes in three phospholipid fatty acid biomarkers were observed among the treatments. These changes indicated that different ATZ-degrading microbial consortia resulted in equivalent ATZ degradation rates between treatments. Results demonstrated that soil microbial response was the dominant mechanism controlling ATZ degradation in the soil studied, rather than root phytochemicals.

Corneal Cross-Linking: An Effective Treatment Option for Pellucid Marginal Degeneration.

Purpose: This is the first review article examining literature specific to the use of corneal cross-linking (CXL) to treat pellucid marginal degeneration (PMD). Results: CXL appears to be an effective treatment that may halt the progression of PMD to stabilize vision. This could postpone or eliminate the need for corneal transplantation in the management of these patients. Furthermore, combining CXL with keratorefractive surgery in a single procedure has been shown to be safe and successful in improving vision in PMD patients. Conclusions: The data reported in literature is limited at this time, consisting mostly of retrospective studies with short term follow up. Further research is needed to evaluate refractive effects of combined CXL and excimer laser procedures.

In vitro transformation of BALB/c-3T3 cells by chlorinated ethanes and ethylenes.

Eight chlorinated ethanes and 3 chlorinated ethylenes were tested in the BALB/c-3T3 cell transformation assay. Under the conditions of the assay, vinyl chloride and 1,1,1-trichloroethane induced a clear positive transformation response while 1,1,2-trichloroethane and trichloroethylene were weakly positive. Chloroethane, 1,1- and 1,2-dichloroethane, 1,1,1,2- and 1,1,2,2-tetrachloroethane, hexachloroethane and tetrachloroethylene were all negative in the assay conducted in the absence of an exogenous metabolic activation system. These results suggest that the BALB/c-3T3 cells possess capability to activate some, but not all, of the chlorinated hydrocarbons which exhibit species specificity in producing carcinogenicity in mice but not in rats.