Prediction of the bioconcentration factor of PCBs in fish using the molecular connectivity index and fragment constant models.

Models based on molecular connectivity index (MCI) and fragment constant (FC) method were developed for prediction of the bioconcentration factor (BCF) for polychlorobiphenyls (PCBs) in fish. The mean residuals for the MCI and FC models were 0.195 and 0.223 log units, respectively. The two models were then compared in terms of their mean residuals. In addition to the chlorine atom substitution number, other important structural features exhibiting a significant influence on the BCFs of PCB congeners were discussed and incorporated to the models. These features include the degree of the ortho-substitution, the presence of chlorine pairs in the three- and five- positions, and the crowding of chlorine atoms on the phenyl ring.     

The Role of Macrophytes in the Retention of Phosphorus in the River Thame,England

The effects of the growth of the dominant species of macrophytes on phosphorus transport in the River Thame, a nutrient enriched lowland clay catchment in southern England, were assessed using a mass-balance approach. Macrophyte abundance was estimated between late March and early June at three sites along the river. the plant biomass of phosphorus and the total phosphorus content of sediments in the main part of the river channel and sediments associated with the plant roots were measured on each occasion. Total phosphorus concentrations in the river water were measured at weekly intervals at a gauging station at the lower end of the study reach.

The results showed that the phosphorus content of plants at the site most impacted by sewage derived phosphorus was < 1% of the flux of total phosphorus estimated for the water column in April and May. Phosphorus contained in the total standing crop of macrophytes at the least impacted site was estimated as approximately 3% of the mean daily flux of total phosphorus in the water. Although no trends were found in the total phosphorus contents of the roots, shoots or sediments through the season, differences in the phosphorus content of the sediments were found between sites with different phosphorus loading. Higher porewater and Equilibrium Phosphate Concentrations (EPC_oS) were recorded at the site most impacted by sewage effluent when compared to an upstream sampling site.     

Agroecosystem functional assessment and its difficulties

Agroecosystem functional assessment indicators provide a necessary bridge between decision-makers and scientists. The development of acceptable indicators, however, remains a difficult task because the current knowledge and understanding of ecosystems is not sufficient to allow an objective assessment of all ecosystem functions. These difficulties were summarized from three perspectives. First, there are difficulties in individual function assessment. Of the four functions associated with agroecosystems-energy flow, materials cycling,information flow and value flow-data on material cycling and information flow remain difficult to obtain and the indicators relatively immature. Secondly, there are difficulties of integration. During the assessment process, the integration of the agroecosystem functions remains the biggest obstacle. Until now, there has been no practical or effective methodology established to resolve the problem. At present, the makeshift approach has been to weight the various indicators and then add them together. Thirdly, there is the problem of obscure concepts and concept confusion. When assessments of agroecosystems are conducted, concepts such as structure, function, benefit,and resource utilization are used extensively. To date, no logical relationship (either real or implied) has been developed between any of these concepts. Are they causes and results such that the relationship between them is linear, or are they independent from one another such that the relationship is parallel? Thus far, the essence of this question is yet to be explored.     

Adsorption and absorption of dichlorodiphenyltrichloroethane (DDT) and metabolites (DDD and DDE) by rice roots

A three-step sequential extraction procedure was applied to measure the concentrations of dichlorodiphenyltrichloroethane (DDT) on rice root surface and in root tissues collected from two sites in Tianjin. Bulk and rhizosphere soils were also analyzed. The measured DDXs in the rhizosphere soils were significantly higher than those in the bulk soils. On average, p,p'-DDT, p,p'-DDD, and p,p'-DDE in the soil accounted for 38%, 47% and 15% of the total. For total DDXs, approximately one third remained on the outer surface of the roots. The partition of DDXs between rhizosphere soil and root surface depend on contaminant affinity to soil organic matter, soil organic matter content and root specific area. A case specific equation was developed to quantitatively describe the partition of DDXs between soil and root surface.     

Objectives,components and experiences in the development of The IOC Marine Pollution Monitoring System (MARPOLMON)

The Marine Pollution Monitoring System (MARPOLMON) constitutes a marine chemical component of the Global Environment Monitoring System (GEMS). The Programme covers all matters related to marine pollution research and associated monitoring activities required for the assessment of marine pollution. MARPOLMON constitutes the data-gathering activity, being directed to accurately determine levels of selected contaminants in several phases of the marine environment in various regions of the World Ocean. It is envisaged to utlize MARPOLMON generated data for the purposes of construction of mass-balances and making contamination and pollution assessments in regional and global contexts.Data gathering, reporting and exchange requires stringent control of the quality of the information retrieved, which in turn dictates the development and testing of standard methodology, its widespread adoption and intercomparison of methods and feedback-refinement of orogonal methods or hypotheses.     

Linking biosensor responses to Cd, Cu and Zn partitioning in soils

Soils bind heavy metals according to fundamental physico-chemical parameters. Bioassays, using bacterial biosensors, were performed in pore waters extracted from 19 contrasting soils individually amended with Cd, Cu and Zn concentrations related to the EU Sewage Sludge Directive. The biosensors were responsive to pore waters extracted from Zn amended soils but less so to those of Cu and showed no toxicity to pore water Cd at these environmentally relevant amended concentrations. Across the range of soils, the solid-solution heavy metal partitioning coefficient (K(d)) decreased (p<0.01) with increasing amendments of Cu and Zn; Cu exhibited the highest K(d) values. Gompertz functions of Cu and Zn, K(d) values against luminescence explained the relationship between heavy metals and biosensors. Consequently, biosensors provide a link between biologically defined hazard assessments of metals and standard soil-metal physico-chemical parameters for determining critical metal loadings in soils.     

Carotenoid-dependent coloration of male American kestrels predicts ability to reduce parasitic infections

The signaling function of sexually selected traits, such as carotenoid-dependent avian plumage coloration, has received a great deal of recent attention especially with respect to parasitism and immunocompetence. We argue that parasite-mediated models of sexual selection may have an implicit temporal component that many researchers have ignored. For example, previous studies have demonstrated that carotenoid-dependent traits can signal past parasite exposure, current levels of parasitism, or the ability of individuals to manage parasitic infections in the future. We examined repeated measures of carotenoid-dependent skin color and blood parasitism in American kestrels (Falco sparverius) to distinguish whether coloration might signal current parasitism or the potential to deal with infections in the future. We found no evidence that coloration was related to current levels of parasitism in either sex. However, coloration of males significantly predicted their response to parasitism; males with bright orange coloration during prelaying, when mate choice is occurring, were more likely than dull yellow males to reduce their levels of infection by the time incubation began. Coloration during prelaying may advertise a male’s health later in the breeding season. For kestrels, the ability to predict future health would be highly beneficial given the male’s role in providing food to his mate and offspring. Coloration of females was not a significant predictor of parasitism in the future, and we provide several possible explanations for this result.     

Salinity-temperature profiles in the Panama Canal Locks

In discussions concerning the possible construction of a Panamá sea-level canal it has been assumed that Gatún Lake, part of the present canal, acts as a fresh-water barrier to the migration of marine animals from either end of the Canal to the other. Methodical documentary salinity determinations have not been made previously, and only a few surface salinity observations have been recorded. Determinations of salinity-temperature profiles made in spring and fall, 1972, show essentially freshwater to be present from Miraflores Lake, through the Pedro Miguel Locks, through Gatún Lake, to, and including, the upper chambers of the Gatún Locks. With the exception of those of the lower chamber of the Miraflores Locks, the profiles indicate homogeneity and thorough vertical mixing of all water masses in the lock systems and lakes of the canal. Homogeneity of the water in the lock chambers is thought to be due to turbulence during filling of the chambers, to the piston-effect of large ships moving into the chambers, to the action of ships' propellers, and to density currents established as the lock gates are opened. Water in the approach channel at the Pacific end appears to be more homogeneous than that at the Atlantic end. The Panama Canal does, in fact, constitute a fresh-water barrier to the migration of the stenohaline marine biota of the Pacific and Atlantic Oceans.