Laboratory degradation studies of 14C-atrazine and -isoproturon in soil from sugarcane cultivated fields under Kenyan tropical conditions.

A study to compare the degradation rates of atrazine (6-chloro-N(2)-ethyl-N(4)-isopropyl-1,3,5-triazine-2,4-diammine) and isoproturon [3-(4-isopropylphenyl)-1,1-dimethylurea] in soils from sugarcane fields with different practices of herbicides application was carried out. (14)C-atrazine was poorly mineralized to (14)CO(2) (1.10% +/- 0.22%) after 139 days of incubation in soil without previous exposure to atrazine. In the same soil also with no previous isoproturon exposure isoproturon was mineralized to (14)CO(2) by 7.70% +/- 0.94%. Atrazine mineralization after 98 days was 13.4% +/- 0.30% in soil which discontinued the use of atrazine in 1997 while it was 89.9% +/- 1.23% in soil in which atrazine is currently being used. The isoproturon mineralization values were 7.24% +/- 0.85% and 22.97% +/- 0.96% in soil which discontinued atrazine and soil currently using atrazine, respectively.

[Identification of 1,2,4-trichlorobenzene-mineralizing bacteria and their function analysis].

Two strains, E3 and F2, capable to mineralize 1,2,4-trichlorobenzene (1,2,4-TCB) were isolated from a chlorinated benzenes contaminated soil using (14)C-1, 2,4-TCB as carbon source. They were identified by their 16S rDNA coding genes and fluoresence in situ hybridization (FISH) analysis as members of the genus Bordetella. A similarity of 100% were observed between strains E3 and F2 with their 16S rDNA sequences. They had the highest homology of 100% with Bordetella sp. QJ2-5 and the closest relation to described species, Bordetella petrii (GDH030510) with a similary of 99.4%. Strains E3 and F2 could degrade about 90% of 1,2,4-TCB and mineralize 58% and 46% of 1,2,4-TCB to CO2 within 30 days in mineral liquid cultures, respectively. Biomass was formed during the mineralization process.

Biomineralisation of 1,2,4-trichlorobenzene in soils by an adapted microbial population.

In laboratory experiments the mineralisation of 14C-labelled 1,2,4-trichlorobenzene (1,2,4-TCB) in soils was studied by direct measurement of the evolved 14CO2. The degradation capacity of the indigenous microbial population was investigated in an agricultural soil and in a soil from a contaminated site. Very low mineralisation of 1% within 23 days was measured in the agricultural soil. Whereas in the soil from the contaminated site the mineralisation occurred very fast and in high rates; up to 62% of the initially applied amount of 1,2,4-TCB were mineralised within 23 days. The transfer of the adapted microbial population into the agricultural soil significantly enhanced the mineralisation of 1,2,4-TCB in this soil, reflecting, that the transferred microbial population survived and maintained its degradation ability in the new microbial ecosystem. Additional nutrition sources ((NH4)2HPO4) increased the mineralisation rates in the first days significantly in the contaminated soil. In the soil from the contaminated site high amounts of non extractable 14C-residues were formed.

Ten-vertex rhodadithiaborane chemistry:.

Neutral 8-(5-iodo-n-pentyl)-3-(eta(5)-pentamethylcyclopentadienyl)-arachno-3-rhoda-7,8-dithiaundecaborane, [Rh(C(5)H(19)B(8)IS(2))(C(10)H(15))], obtained from the [arachno-7,8-S(2)B(9)H(10)](-) anion by treatment with I(CH(2))(5)I followed by [Rh(C(5)Me(5))Cl(2)](2) and N,N,N',N'-tetramethyl-1,8-diaminonaphthalene, has the 11-vertex cluster geometry of [arachno-7,8-S(2)B(9)H(10)](-), but with an [Rh(C(5)Me(5))] unit in the 3-position instead of a [BH] unit, and with a -(CH(2))(5)I chain attached exo to an S atom.

Triple linking of the decaboranyl cluster. Structure of [(SMe2)2B10H10(B10H13)2] as determined by synchrotron X-ray diffraction analysis.

In an attempt to find generic routes to multiple inter-cluster sigma-linking, mild thermolysis of [6,9-(SMe2)2-arachno-B10H12] 1 in inert hydrocarbon solution gives the tridecaboranyl species [6,9-(SMe2)2-arachno-B10H(10)-1,5-(6'-nido-B10H13)2] 3 (23%).

S-triazine residues in groundwater.

In the last years, the occurrence of pesticides and other chemicals in groundwater has been confirmed. The herbicide atrazine is among the pesticides most frequently detected in groundwater. In groundwater samples from the United States atrazine concentrations reached levels up to 10 micrograms/1. In our lysimeter experiments with radioactive labelled terbuthylazine we measured 2.87-4.20% of the applied radioactivity after 1160 days in the leachate.

Mineralization kinetics of chemicals in soils in relation to environmental conditions.

The mineralization kinetics of the detergent n-dodecylbenzenesulfonate ([14C]LAS) and the plasticizer di(2-ethylhexyl)phthalate ([14C]DEHP) were studied in three fresh sampled soils of different type. Time series of 14CO2 evolution were fitted with various linear and nonlinear models. The kinetics could be represented best by a 3/2-order function with linear adaptation and three parameters: x1 describing the gradient of the exponential part of the curve, x2 the lag phase, and x3 the last, asymptotic part. These parameters as well as the maximal degraded amounts (A) were correlated with various environmental conditions. For LAS, A was similar in all three soils and was positively related to pH in two soils and to humidity in one soil (rendzina). The parameters x1-x3 were positively influenced by soil humidity in all three soils. The degraded amounts A, expressed as percentage of added dose, were independent of initial concentration. Both A and the parameters x1-x3 increased with increasing temperature. Degradation was negligible below 3 degrees C. For DEHP, the degradation was much slower than that of LAS and was most rapid and most complete in the rendzina soil. Relative degradation A was lower for higher initial application rates. Temperature influenced both A and the lag phase. Degradation was not significant below 10 degrees C.