No description available.

A herbicidial mixture of diquat and endothall used for control of aquatic macrophytes was evaluated to determine the environmental persistence of the combination and its components and phytotoxicity for egeria (Egeria densa). The tests were conducted in wooden pools illuminated with a 15 hr photoperiod with flourescent lights. Diquat was assayed by a spectrophotometric procedure and endothall was quantified using a gas-liquid chromatographic technique, Persistence of diquat in water was decreased by the addition of plants and sediments to the system; whereas the decline of endothall in water was independent of the presence of plants and sediments at the concentrations tested. No measurable differences existed between the persistence of the mixture under lentic and lotic conditions. The presence of each herbicide in the mixture appeared to decrease the uptake in plants and sediments and increase the persistence of the other herbicide in water. Results of testing the mixture and its components individually under various water hardnesses (32 mg/1 to 460 mg/1) indicate the phytotoxicity of the mixture and diquat decreased as water hardness increased, while the phytotoxicity of endothall remained unchanged. Herbicide concentration decline in water appeared independent of water hardness. While diquat was effective in controlling egeria, endothall was not, indicating that the role of the mixture for treating egeria should be reevaluated. / M.S.

Call number: LD2668 .T4 1964 C74 / Master of Science

No description available.

No description available.

No description available.

No description available.

No description available.

No description available.

Atrazine, a member of the s-triazine herbicides, appears on the EC Red List of chemicals that cause environmental concern, with residues occurring frequently in sub-soils and aquifers world-wide. Microbial metabolism is considered to be the major mechanism of complete removal of atrazine from the soil environment. Laboratory-based studies were carried out to investigate the microbial mineralisation of atrazine in soil, and to develop novel methods for potential acceleration of breakdown. In initial investigations, simple microcosm experiments were carried out to identify the importance of different fractions (water-soluble and water-insoluble) of plant residues to the dynamics, and extent of atrazine mineralisation. The amendment of soil with different plant residue fractions initially inhibited (for the water-soluble fraction) or enhanced (for the water-insoluble fraction) dynamics of atrazine mineralisation. However, by the end of the incubation, there was no overall effect on atrazine mineralisation. This suggested that increasing the soil organic matter content may render the herbicide less bioavailable to the degrader population. Investigations carried out to determine which component of the microbial biomass was more important in atrazine mineralisation showed that substantial removal of the fungal and Gram-negative bacterial population inhibited atrazine mineralisation in the soil. Experiments to selectively enrich the soil for fungal or bacterial atrazine degraders isolated a mixed bacterial culture able to accelerate atrazine mineralisation when inoculated into soil. The effect of the presence of the earthworm Lumbricus terrestris on the indigenous atrazine degrading microflora was investigated. Results indicated that atrazine mineralisation could be accelerated, but this was not primarily due to increases in microbial biomass, but possibly due to physio-chemical changes brought about by the earthworm and subsequent alterations in atrazine bioavailability.