Respiration rates of particulate matter, collected in sediment traps placed 1 m above the sediment during tidal cover at an intertidal site in the upper Bay of Fundy, Canada, were calculated from oxygen and carbon dioxide fluxes. Values decreased from 6 yg C g-' dry wt h-' during midsummer to < 0.5 pg C g-' dry wt h-' in winter. Rates were positively correlated with seasonal changes in temperature with a coefficient equivalent to a Q l o of 2 and with chlorophyll a in settled material. The ratio of total organic carbon in detritus to daily respiration gave first-order decay constants (k) of 2 to 5 yr-' during summer and 0.3 to 1.3 yr-' during winter. Equivalent 95 % decay times (3/k) were 200 to 500 d and 800 to 3800 d , respectively. Respiration of labile organic carbon was calculated from organlc carbon exceeding the seasonal minimum (0.8 % dry wt) and chlorophyll a content. Lower decay times (20 to 40 d) during the summer coincided with low labile organic carbon : chlorophyll a ratios (30 to 50) indicative of freshly produced organic matter
The saturated vapour concentrations at 35" of 21 organo-mercury compounds have been determined by static and dynamic methods and the corresponding partial pressures derived. For 14 of these compounds, together with mercury and mercuric chloride, values at 25' and 45' have also been determined and the constants in the linear pressure-temperature relation calculated. Some correlation between chemical constitution and vapour pressure has been noted. IntroductionDespite their inherent toxicity, the good fungicidal and bactericidal properties of organomercury compounds have encouraged their widespread use in agriculture. To assess the inhalation hazard arising from the use of eradicant sprays and the dressing of stored seed, the clinical data on intrinsic toxicity must be supplemented with knowledge of the approximate volatility of each compound. Since the published vapour pressure data in this field are scanty, it was decided to determine experimentally the saturated vapour concentrations of as many of the organo-mercurials currently in use as could be obtained.Whereas grain is usually stored in a cool atmosphere and the bulk of fruit spraying in this country is over orchard crops, some fungicidal aerosols are employed in greenhouses, notably on tomatoes. Taking into consideration the English climate and the ventilation procedure
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