A laboratory study of the mineralization and binding of 14C-labeled herbicide rimsulfuron in a rendzina soil.

The fate of pyrimidine-2-14C-rimsulfuron in a rendzina soil was investigated using a laboratory microcosm approach. Measurement of CO2 evolution suggested that rimsulfuron applied at 5 times the recommended dose did not affect soil respiration. Under abiotic conditions, no mineralization of 14C-rimsulfuron into 14C-CO2 occurred and under biotic ones it was very low reaching 0.75% of the applied 14C-rimsulfuron after 246 days of incubation. The analysis of data showed that a three-half order model provided the best fit for the mineralization curve. Extractable 14C-residues decreased over time to 70-80% of the applied 14C-rimsulfuron at the end of the incubation. After 246 days of incubation, non extractable residues (NER) accounted for up to 24.7% of the applied 14C-rimsulfuron and were distributed according to organic carbon in soil size fractions, suggesting a progressive incorporation process of NER to soil humus.

Modulation of metabolic activity prevents degradation of sorbed toluene.

The factors affecting the ability of a bacterial species to degrade different amounts of toluene (8.5 to 217 mg/g) sorbed to granular activated carbon (GAC), in an aqueous solution of mineral salts, were investigated. After 144 days the amounts of toluene remaining on one type of GAC ranged from 7.5 to 9.5 mg/g, and the aqueous concentrations of toluene ranged from 2 to 7 micrograms/L. Neither bacterial death nor an inhibition by accumulating by-products could explain why the remaining toluene had not been degraded. However, at these low concentrations of toluene, and probably because of cell starvation, bacteria were observed to be more than 100-times less efficient to degrade toluene than at high concentrations. We propose that this low degradation ability is responsible for the presence of residual toluene on the GAC, and that this mechanism may contribute to the persistence of low concentrations of sorbed pollutants in the environment.

Distribution of Copper and Cadmium Fractions in Two Forest Soils.

Pollution of soil by Cu and Cd seems to be increasing in Switzerland. To know the background concentration in low polluted soil we have measured their concentrations in every horizon and calculated the total amounts. The concentrations were low: the largest concentrations of Cu and Cd occurred in the topsoil of a Typic Dystrochrept (acid brown soil) (13.5 mg kg-1 Cu and 437 µg kg-1 Cd) and in the Oi-Oa-Al and Bh horizons of a Typic Haplorthod (podzol) (up to 16 mg kg-1 Cu and 460 µg kg-1 Cd in Oi), though when corrected by density, concentrations were higher in Al horizon of the Haplorthod and Al and BC of the Dystrochrept. The Dystrochrept was found to contain more of the metals than the Haplorthod. The soil is the main storage compartment of both ecosystems. A six step sequential extraction was applied to evaluate the affinity of metals for the soil constituents and the binding strength to the solid matrix. Water, 0.1 M NaNO3 , 0.1 M hydroxylamine, 1 M hydroxylamine plus acetic acid, H2 O2 and aqua regia were used as successive reagents. Patterns of Cu and Cd distribution in a given soil are different and, to a lesser extent, for a given element the distribution patterns depend on the soil type. Organic matter or Fe and Mn oxides seem to immobilize Cu whereas Cd is associated mainly with Fe and Mn oxides. If the sequential extraction is considered as succession of reagents of increasing strength, then Cd seems to be less strongly bound to soil than Cu and thus more readily solubilized and translocated within soil. The results show the limitations of multistep sequential extraction as a technique for studying metal fractions.

[The perimetric score in Bjerrum's area]. / Le score périmétrique dans l'aire de Bjerrum.

The authors have examined a protocole in automatic perimetry. On glaucoma they have measured, with different instruments, deficits in visual fields in Bjerrum's area. The perimetric score gives them a numeric data which determines rapidly the patient's state. This data may be used on graphics.

[Role of eye manifestations in chlamydioses]. / Place des manifestations oculaires dans les chlamydioses.

Following an up-to-date bacteriological resume, are recalled the most important clinical manifestations presently attributed to C. trachomatis: general manifestations (pulmonary, articular, venereal, congenital, viscereal and others still under discussion); ocular manifestations (trachoma, inclusion conjunctivitis of newborn infants or adults, other ocular affections still under discussion). The main theories are exposed, which try to explain some epidemiological links between all these manifestations.