Rapid development of drug-resistant mutants of poliovirus

Guanidine hydrochloride is a potent inhibitor of poliovirus synthesis in cell culture. However, the viral progeny which do grow in the presence of guani-dine may become approximately 10,000 times more resistant to the drug. The phenomenon of drug resistance poses yet another problem in the search for a satisfactory viral chemotherapeutic agent.     

ACID DEPOSITION DURING TWO CONTRASTING FRONTAL RAINFALL EVENTS

Analysis of the chemical composition of rain at high temporal resolution provides additional information on wet deposition processes. High resolution data was obtained using a microprocessor-based acid rain monitor at two sites in SW Scotland and SE England. Meteorological details of the transport and wet deposition processes during two frontal rain events were examined and related to rainfall composition. Rapid depletions of ion concentrations during heavy rainfall in the first event were interpreted using a rainfall scavenging model. The sub-event data for the second event showed the influence of frontal discontinuities. Increasing ionic concentrations during this second event were attributed both to the change in air mass, and to diminished upwind precipitation scavenging.     

EPISODIC NATURE OF WET DEPOSITION OF ACIDIC MATERIAL AT A SITE IN SOUTH-EAST ENGLAND

The causal factors for episodic deposition of acidic material in rainfall cannot be fully understood from conventional daily network data. A brief review of the meteorological conditions leading to episodes is given. A definition of ‘episodicity’ was considered and applied to a 6 month data set collected at high temporal resolution using a microprocessor based acid rain monitor at a site in south-east England. The deposition was highly episodic for all of the measured variables when data from individual rain events were considered. Combining the data into daily averages resulted in changes of episodicity classification for several chemical species. A large percentage of the total deposition recorded during the field experiment occurred in a 5 day period when there was an independent report of ecological damage at other locations in England. Nitrate deposition showed the highest degree of episodicity with 51% of the 6 month total occurring during the 5 day episode. Meteorological details of the transport and wet deposition processes during this period were examined. Back trajectory analysis indicated that the episode was the result of pollutant loading in eastern and central Europe of the air masses reaching the site together with an absence of upwind precipitation scavenging.