Dechlorination of 1,2,4-trichlorobenzene in the sediment of Ise Bay

The relation between dechlorination activities of 1,2,4-trichlorobenzene and anaerobic microbial activity were studied in the sediment collected at three sites in Ise Bay in Japan. The degradation rate of spiked 1,2,4-trichlorobenzene (3nmol ml⁻¹) ranged from 15 to 35 pmol day⁻¹ ml⁻¹ wet sediment and about 1/3 to 1/2 of degraded the trichlorobenzene was recovered as dechlorinated products. Among the dichlorobenzenes, the 1,2-isomer had the highest and 1,3-isomer had the lowest production rate. Comparing the three sampling sites, the trichlorobenzene degradation and dichlorobenzenes production rates were related to the sulfate reducing activity for the unit number of sulfate reducing bacteria. Production rates of dichlorobenzenes were completely inhibited by adding molybdate (20 mM), nitrate (60 mM), and formaldehyde solution (4 %). These results indicated that dechlorination activity in the Ise Bay sediment was supported by sulfate reduction activity in the sediment, and not supported by any other anaerobic microbial activity.     

Determination of 1‐octanol/water partition coefficients of isocyanate compounds by an HPLC method

The octanol/water partition coefficients (P _ow) of six monoisocyanate and five diisocyanate compounds were determined by high performance liquid chromatograph (HPLC) methods. Two HPLC peaks, a broad tailed peak followed by a sharp one, were observed with all compounds. The later peak was identified as the isocyanate compound. The P _ow value for each isocyanate compound was determined by fitting the capacity factor of the peak to the regression equation drawn from those of reference compounds. The hydrophobic substituent constants for the isocyanate group were calculated with each of the compounds. The value of this constant was strongly dependent on the type of carbon bound to the isocyanate group and the average values for the aromatic and aliphatic isocyanate groups were 0.35 and — 0.52, respectively. Because of the reactivity of those compounds in the aquatic environment, the P _ow has little relevance to calculation of their environmental fate and ecotoxicity.     

Factors affecting the biodegradability of biodegradable polyester in soil

The biodegradabilities of two polyester, P(3HB-co-3HV) and PCL, in soil were studied to examine the factors affecting the biodegradability of biodegradable plastics in soil. The polymers were mixed with soil and the time course of the biodegradation of the polymer was measured by analyzing the residual polymer. The polymer biodegraded little in early period of the test, but did in the first-order kinetics after a certain time which was dependent on the test substance and soil used. The rate constant and the induction period of the biodegradation were determined from the residual curve. The rate constant and the induction period for P(3HB-co-3HV) increased and reached to the constant values with increasing the particle size of the test substance. Both values depended on the kind of test soil and on the sampling date for the same kind of soil. The variation in the biodegradability among the same kind of soil was primarily attributed to the variation in water content of the soil. The rate constant and the induction period of PCL were smaller and longer than P(3HB-co-3HV), respectively.     

Unique bioconcentration characteristics of new aryl fluoroalkyl ethers in common carp (Cyprinus carpio)

The bioconcentration factors (BCFs) of seven new aryl fluoroalkyl ethers--four bis-4-tetrafluoroethoxyphenyl-type (bis-type) compounds and three mono-4-tetrafluoroethoxyphenyl-type (mono-type) compounds--were obtained by bioconcentration tests using common carp. The BCFs of 4 of the 7 ethers were higher than 5000, indicating their high bioconcentration potential. The bioconcentration characteristics of the bis-type compounds were different from those of the mono-type compounds and non-fluoro diphenylmethanes with a similar skeleton structure to the bis-type compounds, in taking longer to reach a plateau and having a slower elimination rate and in their distribution patterns in the fish body. The BCF of 1 bis-type compound was much higher than the value predicted by an accepted correlation equation between BCF and P(ow). In addition, the logP(ow) of the bis-type compounds calculated by commercially available computer software was remarkably different from that measured.     

Vertical profiles of organochlorine pesticides in sediment core from Nile river and Manzala lake,Egypt

Residue levels of organochlorine pesticides (DDTs, HCHs, HCB and chlordane compounds) were determined in core samples collected from Nile River near by Cairo and Manzala Lake, Egypt in 1994. Regional difference and vertical profiles were discussed in view of historical reconstruction of environmental pollution by these chemicals. On the basis of estimated sedimentation rate (0.5 to 0.7 cm/year) in Manzala Lake, it seems that discharge of DDTs and CHLs into Egyptian environment increased rapidly from early 1960's and the maximum discharge was recorded in 1980's. However, concentration of HCHs increased continuously up to the present in spite of decreasing of DDTs and CHLs after 1980's. It was revealed that vertical profiles of organochlorine pesticides in sediment core from Manzala Lake are useful to estimate a temporal trend of pesticide use in Egypt.     

Food webs are built up with nested subwebs

Nested structure, in which specialists interact with subsets of species with which generalists interact, has been repeatedly found in networks of mutualistic interactions and thus is considered a general feature of mutualistic communities. However, it is uncertain how exclusive nested structure is for mutualistic communities since few studies have evaluated nestedness in other types of networks. Here, we show that 31 published food webs consist of bipartite subwebs that are as highly nested as mutualistic networks, contradicting the hypothesis that antagonistic interactions disfavor nested structure. Our findings suggest that nested networks may be a common pattern of communities that include resource-consumer interactions. In contrast to the hypothesis that nested structure enhances biodiversity in mutualistic communities, we also suggest that nested food webs increase niche overlap among consumers and thus prevent their coexistence. We discuss potential mechanisms for the emergence of nested structure in food webs and other types of ecological networks.