Monte Carlo simulation of dose coefficients for a fish eye lens model exposed to monoenergetic electrons.

Vision is an important sense for the majority of the wildlife species, affecting their ability to find food and escape predation. Currently, no study on radiation induced cataract frequency on the fish eyes lens has been done. However, any thorough future study of this subject will require more accurate dose estimates for the fish eye lens than those currently available. For this purpose, the eye lens absorbed dose per unit fluence conversion coefficients for electron irradiation were calculated using the MCNPX Monte Carlo radiation transport code package. All results were validated against three different fish voxel models. The discrepancies between model results mainly originate from the different fish eye dimensions used in the different studies and in two of the cases the lack of a defined eye lens region. The dose conversion coefficients calculated in this work can be used to estimate the dose to the fish eye lens based on the activity concentration of the surrounding water. The model developed in this work has also demonstrated that the mathematical models still have several advantages over the voxel models.

Effects of pig slurry on the sorption of sulfonamide antibiotics in soil.

Sorption of p-aminobenzoic acid (pABA) and five sulfonamide antibiotics to loess Chernozem topsoil amended with varied additions of pig slurry was investigated in batch trials. In unfertilized soil, partition coefficients (Kd) of sulfonamides ranged from 0.3 to 2.0. Strong sorption nonlinearity (1/n = 0.5 to 0.8) was best fitted by the Freundlich isotherm (R2 = 0.7 to 1.0) and was indicative for specific sorption mechanisms. Adsorption to pig slurry was much stronger, and nondesorbable portions were increased compared with soil. However, in a mixture of soil and slurry (50:1 w/w), sorption of the antibiotics was significantly decreased at a lower concentration range of pABA and the sulfonamides. This was attributed to competitive adsorption of dissolved organic matter (DOM) constituents from manure. An increase in pig slurry amendment resulted in increased total organic matter, DOM concentration, and ionic strength, but pH decreased. As a result, the nonadsorbed portions of pABA, sulfanilamide, and sulfadiazine (logD(ow) < -0.4) ranged from 47% to 82% of the applied concentration in the differently manured substrates. Dissolved fractions of the antibiotics reached a maximum at a soil-slurry ratio of 9:1 and decreased with further addition of manure. This decrease was related to the formation of less-effective DOM associates in solution. The adsorbed and desorbed portions of the less-polar substances--sulfadimidine, sulfadimethoxine, and sulfapyridine (logD(ow) > 0.1)--remained nearly constant in the presence of increased manure input. The pH changes caused by manure amendment strongly affected ionisation status of the latter compounds, thus resulting in increased adsorption, which compensated the mobilizing effect of DOM. It is suggested that the effect of manure be considered in test methods to determine the soil retention of pharmaceutical substances.