Bioavailability of HOC depending on the colloidal state of humic substances: a case study with PCB-77 and Daphnia magna

Condensed organic matter with higher affinity for hydrophobic organic compounds (HOC) is currently held responsible for slow desorption and concomitant lower bioavailabilities of HOC in sediments and soils. In an experiment with Daphnia magna and IHSS Peat Humic Acid (PHA), we showed that the bioconcentration factor (BCF) of 3,3',4,4'-tetrachlorobiphenyl (PCB-77) was directly related to the charge of the humic colloid, as predicted by the metal-humic binding model WHAM. Consistent with the type of binding to the humic acid (counter-ion accumulation vs. specific binding), increasing the concentration of Na+ and Ca2+ ions generated opposite effects on colloid charge and HOC binding by the humic acid. Condensation as a colloidal phenomenon in solution as well as on surfaces needs to be addressed as a contributor to lower bioavailabilities and, possibly, to slower desorption kinetics.     

Ambient ozone (O3) and adverse crop response: a unified view of cause and effect

This paper presents a cohesive view of the dynamics of ambient O(3) exposure and adverse crop response relationships, coupling the properties of photochemical O(3) production, flux of O(3) from the atmosphere into crop canopies and the crop response per se. The results from two independent approaches ((a) statistical and (b) micrometeorological) were analyzed for understanding cause-effect relationships of the foliar injury responses of tobacco cv Bel-W3 to the exposure dynamics of ambient O(3) concentrations. Similarly, other results from two independent approaches were analyzed in: (1) establishing a micrometeorological relationship between hourly ambient O(3) concentrations and their vertical flux from the air into a natural grassland canopy; and (2) establishing a statistical relationship between hourly ambient O(3) concentrations in long-term, chronic exposures and crop yield reductions. Independent of the approach used, atmospheric conditions appeared to be most conducive and the crop response appeared to be best explained statistically by the cumulative frequency of hourly ambient O(3) concentrations between 50 ppb and 90 ppb (100 and 180 microg m(-3)). In general, this concentration range represents intermediate or moderately enhanced hourly O(3) values in a polluted environment. Further, the diurnal occurrence of this concentration range (often approximately between 0900 and 1600 h in a polluted, agricultural environment) coincided with the optimal CO(2) flux from the atmosphere into the crop canopy, thus high uptake. The frequency of occurrence of hourly O(3) concentrations > 90 ppb (180 microg m(-3)) appeared to be of little importance and such concentrations in general appeared to occur during atmospheric conditions which did not facilitate optimal vertical flux into the crop canopy, thus low uptake. Alternatively, when > 90 ppb (180 microg m(-3)) O(3) concentrations occurred during the 0900-1600 h window, their frequency of occurrence was low in comparison to the 50-90 ppb (100-180 microg m(-3)) range. Based on the overall results, we conclude that if the cumulative frequency of hourly ambient O(3) concentrations between 50-62 ppb (100-124 microg m(-3)) occurred during 53% of the growing season and the corresponding cumulative frequency of hourly O(3) concentrations between 50-74 ppb (100-148 microg m(-3)) occurred during 71% of the growing season, then yield reductions in sensitive crops could be expected, if other factors supporting growth, such as adequate soil moisture are not limiting.     

A comparative ecological study on the scyphozoans Aurelia aurita,Cyanea capillata and C. lamarckii in the Gullmar Fjord,western Sweden, 1982 to 1986

During the years 1982 to 1986, the life cycles and population dynamics of three scyphozoans, Aurelia aurita (L.), Cyanea capillata (L.) and C. lamarckii (Person and Lesueur), were studied in the Gullmar Fjord on the Swedish west coast. The settling of planulae, strobilation of scyphistomae and release of ephyrae were followed on ceramic settling plates in the laboratory and in the field. Weekly to bi-weekly hauls with Bongo nets were used to study the abundance of ephyrae and medusae. The results show great differences in the life cycles and ecology of the three species. A. aurita utilizes the best season for scyphistoma growth (August to September) and strobilates during the highest zooplankton abundance in October. C. capillata strobilates during the spring (March to May), and the abundance of C. capillata medusae is more dependent on immigration from the North Sea than A. aurita. C. lamarckii does not reproduce at all in the Gullmar Fjord and is totally dependent on immigration from the North Sea. The possibility of interspecific competition between A. aurita and C. capillata is discussed. A preliminary experiment showed that scyphistomae of A. aurita eat planula larvae of C. capillata during the autumn.     

Do Midas cichlids win through prowess or daring? It depends

Summary Individual Midas cichlids (Cichlasoma citrinellum) show persistent differences in aggressive behavior toward dummy fish. The starting question was whether the level of such behavior can be used to predict the winner of a fight. In the first (long-term) experiment two fish were matched for size, color, and sex. After 24 h the opaque barrier separating the 2 fish was removed; they immediately behaved aggressively. Scores for aggression toward dummies did not predict the winners, nor did taking the initiative in escalation. But weight did foretell the winners, who averaged only 2% heavier than their opponents. The conventional display phase of such fights was brief (20% of total duration), and escalation was rapid. Both winners and losers sustained damage, but losers accumulated damage faster than winners. In the subsequent (short-term) experiment the fish were separated only 1–2 h. Now aggression scores predicted winners, and winners were the fish who escalated. Weight of fish had no effect. The conventional phase was relatively much longer, about half the length of the fight. Losers accumulated damage at the same rate as the losers in the long-term experiment, but the fights were shorter; winners suffered little damage. The fish had difficulty assessing one another. Fighting prowess was remarkably uniform when weight was factored out. Daring to escalate, in contrast, varied among individuals and correlated with aggression scores. Prowess (=weight) determined the outcome in the long-term experiment, which may find its parallel in nature in intraterritorial disputes. Daring to escalate determined the winner in the short-term experiment; this may be comparable to establishing a territory in nature.Prowess probably results from strong directional selection because it has low costs and high benefits. In contrast, daring is subject to bi-directional selection because both costs and benefits are high. Resource holding potential is conventionally viewed as deriving from prowess of self and opponent and value of resource; to that one must add the individual's inherent aggressiveness.     

Air pollution exposure monitoring and estimation. Part V. Traffic exposure in adults

In Oslo, traffic has been one of the dominating sources of air pollution in the last decade. In one part of the city where most traffic collects, two tunnels were built. A series of before and after studies was carried out in connection with the tunnels in use. Dispersion models were used as a basis for estimating exposure to nitrogen dioxide and particulate matter in two fractions. Exposure estimates were based on the results of the dispersion model providing estimates of outdoor pollutant concentrations on an hourly basis. The estimates represent concentrations in receptor points and in a square kilometre grid. The estimates were used to assess development of air pollution load in the area, compliance with air quality guidelines, and to provide a basis for quantifying exposure-effect relationships in epidemiological studies. After both tunnels were taken in use, the pollution levels in the study area were lower than when the traffic was on the surface (a drop from 50 to 40 micrograms m-3). Compliance with air quality guidelines and other prescribed values has improved, even if high exposures still exist. The most important residential areas are now much less exposed, while areas around tunnel openings can be in periods exposed to high pollutant concentrations. The daily pattern of exposure shows smaller differences between peak and minimum concentrations than prior to the traffic changes. Exposures at home (in the investigation area) were reduced most, while exposures in other locations than at home showed only a small decrease. Highest hourly exposures are encountered in traffic.     

Multivariate analysis of accumulation and critical risk analysis of potentially hazardous elements in forage crops

Environmental Monitoring and Assessment - Few estuaries remain unaffected by water management and altered freshwater deliveries. The Caloosahatchee River Estuary is a perfect case study for...