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1.
Surface soil and sediment samples were collected from the surroundings of the Ittehad Chemical Industries Kalashah Kaku industrial zone to assess residual level of 19 organochlorine pesticides (OCPs) and identify their sources. DDTs and HCHs were most prevalent OCPs and general pattern of contamination followed the order: ∑DDT > ∑HCH > dicofol > endrin > heptachlor > dieldrin > endosulfan II. Total measured concentrations of HCHs (6.38–121.71 ng/g) and DDTs (759.65–1811.98 ng/g) were greater in the soil samples collected from fodder/rice fields irrigated with the factory effluents and in the surrounding of waste disposal site. Ratios of β to γ-HCH highlighted an old mixed source of technical HCH and lindane in surface soils. Predominance of p,p′-DDT and p,p′-DDE among isomers and metabolites showed that large quantity of technical grade DDT is still present in the surrounding surface soils. Six soil samples were categorized as heavy polluted soils (class III category of DDT > 1,000 ng/g), two soil samples into less polluted soil between class I and II (50–500 ng/g) and 28 soil samples as non-polluted (<50 ng/g) according to environmental quality standards for surface soils. Six soil samples were categorized as less polluted between class I and II of HCHs (50–500 ng/g). Greater concentration of DDTs and HCHs above quality guideline poses potential exposure risk to biological organisms, safety of agricultural products and human health in the surrounding of the Ittehad Chemical Industries.  相似文献   

2.
Soil residual concentration of organochlorine pesticides (OCPs) were determined in 245 agricultural surface soil samples collected from Chengdu Economic Region, Sichuan Province, Southwest China, in order to investigate their spatial distribution and the controlling environmental factors. Results showed that detectable ratios of hexachlorocyclohexane (HCH) and dichlorodiphenyltrichloroethane (DDT) were very high, ranging from 88.16 (for δ-HCH) to 97.96% (for p,p′-DDE). The concentrations of DDTs were higher than HCHs, which were consistent with their historical usage in China. OCPs concentrations in the economically developed regions (Chengdu Plain) were higher than in the less developed, mountainous region around Chengdu Plain. The metabolite to parent ratio analysis of HCHs and DDTs indicated there were new pesticide inputs, possibly from the use of lindane (γ-HCH) and dicofol in some regions although they have banned for agricultural use since 1983. Also, the distribution of OCP congeners in soil was mainly governed by their individual physical and chemical characteristic, historical usage amount and patterns, and the environmental conditions, such as, temperature, landform, soil type, etc.  相似文献   

3.
北京市有机氯农药填图与风险评价   总被引：2，自引：0，他引：2  
采用1个样/km2的密度、1个分析组合样/16km2的方法,对北京市784km2范围内的土壤、大气干湿沉降物、大气颗粒物中HCH、DDT的含量和空间分布特征进行有机氯农药填图.查明2000年北京市地表土壤HCH和DDT的平均含量分别为8.80±11.83ng/g、108.99±301.90ng/g.2006年大气干湿沉降物中HCH和DDT平均含量分别为10.09±9.60ng/g、12.99±13.51ng/g,HCH和DDT的年沉降通量分别为996.57±939.96g/a·km2、1291.53±1342.28g/a·km2.2006年大气颗粒物PM10和PM2.5中的HCH含量分别为0.294±0.205ng/m3和0.217±0.137ng/m3,DDT的平均含量分别为1.037±1.301ng/m3和0.522±0.773ng/m3,显著高于2002-2003年度大气颗粒物中HCH(PM100.01786ng/m3,PM250.01731ng/m3)和DDT(PM100.01672ng/m3,PM2.50.02353ng/m3)的含量,表明北京市或周边地区仍在使用含HCH和DDT化学成分的农药.以2000年北京地表土壤和2006年大气干湿沉降物中HCH和DDT的含量为基础,对2020年土壤中HCH和DDT的时空演变的预测显示,即使干湿沉降物中HCH和DDT的沉降通量每年以5%的速率递减,到2020年土壤中HCH和DDT的环境质量仍不能显著改善,而控制和削减北京及周边地区含HCH和DDT成分农药的使用将是改善北京地表土壤环境质量的关键措施.  相似文献   

4.
Endosulfan, a chlorinated cyclodiene insecticide is of environmental concern because of its apparent persistence and toxicity to many non target organisms. Endosulfan is hydrophobic and persists in soil for more than a year. To overcome the problem of hydrophobic and limited availability, surfactants play a major role in soil remediation. In the present study, the effect of Tween 80 added to the soil on the degradation of endosulfan by Pseudomonas aeruginosa at different pH (7.0 and 8.5) was studied. The addition of synthetic surfactant Tween 80 enhanced the solubility and degradation of endosulfan. A significant degradation (94%) was observed in pH 8.5 and Tween 80 added soil; the bacterial population in the treatment unit T8 was 75 × 109 CFU/g of soil. The unit T4 inoculated at pH 8.5 showed 86 % alpha and 60 % beta endosulfan degradation, the bacterial population was 73 × 108 CFU / g of soil. The degradation of both the isomers were observed and accompanied with formation of endodiol and endosulfan sulfate.  相似文献   

5.
北京郊区地表水中有机氯农药残留水平及特征   总被引：5，自引：0，他引：5  
有机氯农药滴滴涕(DDT)、六六六(HCH)等化学性质非常稳定,很难生物降解,对环境及人类健康构成了严重威胁。尽管我国从1983年起已禁止使用,但现在的土壤、水等环境样品中仍有不同程度的检出。水资源是自然环境的主要组成要素,又是农业生产的重要自然资源。以往已有学者对北京部分河流地表水中有机氯农药残留进行过研究,发现存在不同程度水体污染。近年来,经过各方大力控制水体污染和环境治理,北京地区地表水中仍有有机氯农药残留,其残留现状是人们十分关心的重要问题。因此本文选择北京郊区为研究区域,采集了温榆河、北运河、延庆、房山、昌平、顺义等地区地表水,分析了水体中DDTs和HCHs污染物的含量以及分布情况,结果表明DDTs、HCHs在北京郊区地表水中均有不同程度的检出,DDTs含量为ND~1398 ng/L,HCHs含量为387~14642 ng/L。本文同时研究了DDT与其代谢产物DDE、DDD的组成比例以及HCH同分异构体的组成特征,对北京郊区地表水中DDTs和HCHs的污染来源进行了简要分析。  相似文献   

6.
Summary. Most currently used techniques for analysing the stability of near surface structures, such as rock slopes, are based on the application of the effective Coulomb shear strength parameters cohesion c′, and the angle of friction φ′ on some known or anticipated shear surface subjected to an effective normal stress σ′n. The most widely used of these techniques are the variants of the method of slices and related upper bound techniques. If the Hoek-Brown criterion is to be used to model the strength of near surface fractured rocks, it is necessary to determine equivalent Coulomb shear strength parameters for the specified level of effective normal stress. Calculation of the equivalent Coulomb parameters for the Hoek-Brown criterion for cases when a ≠ 0.5 is not a straightforward matter. A simple procedure for calculating instantaneous values of c′i and φ′i has been developed based on spreadsheet calculations and the application of a numerical optimisation routine. This procedure can also be applied to calculating the Hoek-Brown envelope plotted in shear stress/normal stress space. A simple closed form solution for c′i and tan φ′i has also been developed for the special case when a = 1. A three-dimensional version of the Hoek-Brown criterion has been developed by combining it with the Drucker-Prager criterion. This new yield criterion has been implemented by numerical solution of the governing equations. A simplification of this three-dimensional yield criterion has been developed by introducing an intermediate principal stress weighting factor. Comparison with published results demonstrates that this simplified criterion has the capacity to model the results of true triaxial tests for a range of different rock types over a wide range of stress levels. The new three-dimensional yield criterion has the advantage that its input parameters can be determined from routine uniaxial compression tests and mineralogical examination.  相似文献   

7.
Investigation of sediment samples from Sites 1039 and 1040 (ODP Leg 170) drilled off the Nicoya peninsula (Costa Rica) by organic geochemical and organic petrological methods has revealed that subduction has only little influence on the composition of the sedimentary organic matter. Organic carbon contents reached 1.5% in the Pleistocene samples but Miocene and Pliocene sediments had an average organic carbon content of less than 0.5%. Organic carbon/sulfur ratios are generally below 2.8, reflecting an intense sulfate reduction in the uppermost sediments which was enhanced by sulfate supply both from sea water and deeper strata. Microscopical examinations indicate that the organic matter is mainly derived from marine sources. A small amount of terrigenous organic matter is, however, present as well according to n-alkane and fatty acid distributions. The alkenone unsaturation index U37k′ shows only a slight decrease during the Miocene and Pliocene, and stronger variations in the Pleistocene, probably indicating more stable sea surface temperatures during the Miocene and Pliocene. Variations in the Pleistocene can possibly be related to glacial/interglacial changes.  相似文献   

8.
In normal faulting regimes, the magnitudes and orientations of the maximum and minimum principal compressive stresses may be known with some confidence. However, the magnitude of the intermediate principal compressive stress is generally much more difficult to constrain and is often not considered to be an important factor. In this paper, we show that the slip characteristics of faults and fractures with complex or nonoptimal geometry are highly sensitive to variation or uncertainty in the ambient effective intermediate principal stress (σ′2). Optimally oriented faults and fractures may be less sensitive to such variations or uncertainties. Slip tendency (Ts) analysis provides a basis for quantifying the effects of uncertainty in the magnitudes and orientations of all principal stresses and in any stress regime, thereby focusing efforts on the most important components of the system. We also show, for a normal faulting stress regime, that the proportion of potential surfaces experiencing high slip tendency (e.g., Ts ≥ 0.6) decreases from a maximum of about 38% where σ′2 = σ′3, to a minimum of approximately 14% where σ′2 is halfway between σ′3 and σ′1, and increases to another high of approximately 29% where σ′2 = σ′1. This analysis illustrates the influence of the magnitude of σ′2 on rock mass strength, an observation previously documented by experimental rock deformation studies. Because of the link between fault and fracture slip characteristics and transmissivity in critically stressed rock, this analysis can provide new insights into stress-controlled fault transmissivity.  相似文献   

9.
The stable carbon isotopic compositions of free and sulfur (S)-bound biomarkers derived from algae, (cyano)bacteria, archaea and higher plants and total organic carbon (TOC) during the first phase of the late Cenomanian/Turonian oceanic anoxic event (OAE) were measured in black shales deposited in the southern proto-Atlantic Ocean in the Cape Verde basin (DSDP Site 367) to determine the response of these organisms to this major perturbation of the global carbon cycle resulting from widespread burial of marine organic matter. The average positive isotope excursions of TOC and biomarkers varied from 5.1‰ to 8.3‰. The δ13C values were cross correlated to infer potential common sources of biomarkers. This revealed common sources for C31 and C32 hopanes but no 1:1 relationship for pristane and phytane. The correlation of δ13CTOC with the δ13C value of sulfur (S)-bound phytane is the strongest. This is because S-bound phytane is derived from phytol that originates from all marine primary producers (algae and cyanobacteria) and thus represents a weighted average of their carbon isotopic compositions. The δ13C values of S-bound phytane and C35 hopane were also used to estimate pCO2 levels. Before the OAE burial event, pCO2 levels are estimated to be ca. 1300 ppmv using both biomarkers and the independent maximum Rubisco fractionation factors. At times of maximum organic carbon burial rates during the OAE, reconstructed pCO2 levels are estimated to be ca. 700 ppmv. However, compared to other C/T OAE sections the positive isotope excursion of S-bound phytane is also affected by an increased production during the OAE. When we compensate for this, we arrive at pCO2 levels around 1000 ppmv, a reduction of ca. 25%. This indicates that burial of organic matter can have a large effect on atmospheric CO2 levels.  相似文献   

10.
A note on fault reactivation   总被引：2，自引：0，他引：2  
Reactivation of existing faults whose normal lies in the σ1′σ3′ plane of a stress field with effective principal compressive stresses σ1′ >σ2′ >σ3′ is considered for the simplest frictional failure criterion, τ = μσn′ = μ(σn − P), where τ and σn are respectively the shear and normal stresses to the existing fault, P is the fluid pressure and μ is the static friction. For a plane oriented at θ to σ1′, the stress ratio for reactivation is (σ1′/σ3′) = (1 + μ cot θ)/(1 − μ tan θ). This ratio has a minimum positive value at the optimum angle for reactivation given by (1/μ) but reaches infinity when θ = 2θ*, beyond which σ3′ < 0 is a necessary condition for reactivation. An important consequence is that for typical rock friction coefficients, it is unlikely that normal faults will be reactivated as high-angle reverse faults or thrusts as low-angle normal faults, unless the effective least principal stress is tensile.  相似文献   

11.
Crystals of hydronium jarosite were synthesized by hydrothermal treatment of Fe(III)–SO4 solutions. Single-crystal XRD refinement with R1=0.0232 for the unique observed reflections (|Fo| > 4F) and wR2=0.0451 for all data gave a=7.3559(8) Å, c=17.019(3) Å, Vo=160.11(4) cm3, and fractional positions for all atoms except the H in the H3O groups. The chemical composition of this sample is described by the formula (H3O)0.91Fe2.91(SO4)2[(OH)5.64(H2O)0.18]. The enthalpy of formation (Hof) is –3694.5 ± 4.6 kJ mol–1, calculated from acid (5.0 N HCl) solution calorimetry data for hydronium jarosite, -FeOOH, MgO, H2O, and -MgSO4. The entropy at standard temperature and pressure (So) is 438.9±0.7 J mol–1 K–1, calculated from adiabatic and semi-adiabatic calorimetry data. The heat capacity (Cp) data between 273 and 400 K were fitted to a Maier-Kelley polynomial Cp(T in K)=280.6 + 0.6149T–3199700T–2. The Gibbs free energy of formation is –3162.2 ± 4.6 kJ mol–1. Speciation and activity calculations for Fe(III)–SO4 solutions show that these new thermodynamic data reproduce the results of solubility experiments with hydronium jarosite. A spin-glass freezing transition was manifested as a broad anomaly in the Cp data, and as a broad maximum in the zero-field-cooled magnetic susceptibility data at 16.5 K. Another anomaly in Cp, below 0.7 K, has been tentatively attributed to spin cluster tunneling. A set of thermodynamic values for an ideal composition end member (H3O)Fe3(SO4)2(OH)6 was estimated: Gof= –3226.4 ± 4.6 kJ mol–1, Hof=–3770.2 ± 4.6 kJ mol–1, So=448.2 ± 0.7 J mol–1 K–1, Cp (T in K)=287.2 + 0.6281T–3286000T–2 (between 273 and 400 K).  相似文献   

12.
Thermal maturity was determined for about 120 core, cuttings, and outcrop samples to investigate the potential for coalbed gas resources in Pennsylvanian strata of north-central Texas. Shallow (< 600 m; 2000 ft) coal and carbonaceous shale cuttings samples from the Middle-Upper Pennsylvanian Strawn, Canyon, and Cisco Groups in Archer and Young Counties on the Eastern Shelf of the Midland basin (northwest and downdip from the outcrop) yielded mean random vitrinite reflectance (Ro) values between about 0.4 and 0.8%. This range of Ro values indicates rank from subbituminous C to high volatile A bituminous in the shallow subsurface, which may be sufficient for early thermogenic gas generation. Near-surface (< 100 m; 300 ft) core and outcrop samples of coal from areas of historical underground coal mining in the region yielded similar Ro values of 0.5 to 0.8%. Carbonaceous shale core samples of Lower Pennsylvanian strata (lower Atoka Group) from two deeper wells (samples from ~ 1650 m; 5400 ft) in Jack and western Wise Counties in the western part of the Fort Worth basin yielded higher Ro values of about 1.0%. Pyrolysis and petrographic data for the lower Atoka samples indicate mixed Type II/Type III organic matter, suggesting generated hydrocarbons may be both gas- and oil-prone. In all other samples, organic material is dominated by Type III organic matter (vitrinite), indicating that generated hydrocarbons should be gas-prone. Individual coal beds are thin at outcrop (< 1 m; 3.3 ft), laterally discontinuous, and moderately high in ash yield and sulfur content. A possible analog for coalbed gas potential in the Pennsylvanian section of north-central Texas occurs on the northeast Oklahoma shelf and in the Cherokee basin of southeastern Kansas, where contemporaneous gas-producing coal beds are similar in thickness, quality, and rank.  相似文献   

13.
Isolation and degradation ability of the DDT-degrading bacterial strain KK   总被引：1，自引：1，他引：0  
A 1,1,1-trichloro-2,2-bis(4-chlorophenyl)ethane (DDT)-degrading bacterium was isolated from soil samples that had been enriched with DDT over a prolonged period of time; these samples were collected from the sewer sludge of a pesticide factory and from DDT-contaminated fields. This consortium was acclimated by repeated passage through a mineral salt medium containing increasing concentrations of DDT. We examined the effects of various factors such as the pH, temperature, concentration of DDT, and the presence of an additional carbon source on the degradation rate of DDT. Based on the analysis of the phenotype, physiological and biochemical characteristics, and 16S rDNA, the strain KK was identified to belong to the bacteria Alcaligenes. The results showed that at the end of 10 days, the rate of degradation of DDT by the strain KK was 66.5%. When the additional carbon source concentration, pH, concentration of DDT, and cultivation temperature is 0.5%, 6, 10 mg l−1, and 30°C, respectively, the biodegradation rate peaks. The results also suggested that (1) bacterial growth increases positively with an increase in the carbon source concentration; (2) the appropriate pH is between 8.0 and 10.0; and (3) the optimal temperature and DDT concentration are 30°C and 10 mg l−1, respectively.  相似文献   

14.
This research was conducted in an attempt to assess the concentration levels and potential sources of organochlorine pesticides (OCPs) in the karst soils of Dashiwei tiankeng, southwest China. The tiankeng is a karst surface expression that can act as a focal point for introduction of contaminants to groundwater system, which may serve as condenser and receiver for semi-volatile persistent organic pollutants such as OCPs. In this study, surface soil samples from Dashiwei tiankeng were collected and 23 organochlorine pesticide compounds were analyzed. The results showed that the concentration was 0.019–3.605 ng/g for DDTs (sum of p,p’-DDD, p,p’-DDE, o,p’-DDT, p,p’-DDT), 0.001–0.218 ng/g for HCHs (sum of α-, β-, γ-, δ-HCH), 0.003–0.290 ng/g for CHLs (sum of heptachlor, heptachlor epoxide, TC, CC and trans-nonachlor), 0.001–0.064 ng/g for endosulfan (sum of α-endosulfan and β-endosulfan), 0.008–1.630 ng/g for HCB and 0.023–0.928 ng/g for other OCPs (sum of aldrin, dieldrin, methoxychlor, endrin, endrin aldehyde and endrin ketone). The total OCPs concentrations varied from 0.055 to 5.216 ng/g. The ratio of DDT/(DDE + DDD) in the floor soils of Dashiwei tiankeng ranged from 0.434 to 0.797, suggesting a mostly historical residue of technical DDT contamination. However, the ratio of DDT/(DDE + DDD) in the upper rim soils was higher than one, which that there was fresh DDT application nearby. Both the floor and upper rim soils of Dashiwei tiankeng had high ratios of o,p’-DDT/p,p’-DDT (range of 0.016–10.833 with mean of 5.424 and 4.667–7.714 with mean of 5.723, respectively), which implied that the primary source of DDTs was probably from dicofol-type DDT products. The average ratios of α-/γ-HCH were 24.435 in the floor soils and 1.067 in the upper rim soils, together with the averaged percentages of β-HCH among the total HCH isomers (accounting for 33.772 %), indicating that the HCHs were a dominant contribution from technical HCH usage in the past.  相似文献   

15.
Beginning with the Swabian Jura earthquake in 1911 the seismic activity in Central Europe is concentrated to this area. A comparison with other events of the same epicentral region shows that the largest earthquake in Germany has the character of a left-lateral horizontal strike slip striking N — NNE. The focal parameters can be assumed within the following intervalls: Seismic moment Mo = 1…8·1017 Nm; focal area Fo = 18…53 km2; average dislocation do = 20…53 cm and stress drop Δpo = 13…19 bar.  相似文献   

16.
Summary The crystal structure of scotlandite —a=4.505(2),b=5.333(2),c=6.405(6) Å, =106.24(3)o; space groupP21/m; cell content 2 {PbSO3} — was determined from singlecrystal X-ray diffractometer data. Scotlandite is isotypic with molybdomenite, PbSeO3. Lead is coordinated to nine oxygen atoms with Pb-Oav=2.75 Å, and possibly further to one sulphur atom with Pb–S=3.46 Å. The average S–O distance in the pyramidal SO3 group is 1.52 Å. The structural relationships to cerussite, PbCO3, are discussed.
Die Kristallstruktur des Scotlandits, PbSO3
Zusammenfassung Die Kristallstruktur des Scotlandits —a=4,505(2),b=5,333(2),c=6,405(6) Å, =106,24(3)o; RaumgruppeP21/m; Zellinhalt 2 {PbSO3} — wurde aus Einkristall-Röntgendiffraktometerdaten bestimmt. Scotlandit ist mit Molybdomenit, PbSeO3, isotyp. Blei wird von neun Sauerstoffatomen mit Pb–Oav=2,75 Å und möglicherweise zusätzlich von einem Schwefelatom mit Pb–S=3,46 Å koordiniert. Der durchschnittliche S–O-Abstand in der pyramidalen SO3-Gruppe mißt 1,52 Å. Die strukturellen Beziehungen zu Cerussit, PbCO3, werden diskutiert.

With 2 Figures  相似文献   

17.
襄樊市郊土壤有机氯农药的地球化学变化   总被引：1，自引：1，他引：0  
采用水平剖面、垂直剖面现场采样及室内测试方法,分析了襄樊市郊代表性经济作物基地HCH和DDT的土壤地球化学变化。结果表明,在垂直方向上,α-HCH/γ-HCH、DDE/DDD比值在土壤20 cm处有明显的分界线;随土壤深度增加,HCHs总量逐渐降低。在水平方向上,同点表层土壤(0~5 cm)的α-HCH/γ-HCH比值大于下层土壤(5~20 cm)的比值或者相差不大。  相似文献   

18.
Coaly source rocks are sufficiently different from marine and lacustrine source rocks in their organic matter characteristics to warrant separate guidelines for their assessment using Rock-Eval pyrolysis. The rank threshold for oil generation is indicated by the increase in BI (S1/TOC) at Rank(Sr)9–10 (Tmax 420–430 °C, Ro 0.55–0.6%), and the threshold for oil expulsion is indicated by the peak in QI ([S1+S2]/TOC) at Rank(Sr)11–12.5 (Tmax 430–440 °C, Ro 0.65–0.85%). The pronounced rank-related increase in HI (S2/TOC) prior to oil expulsion renders the use of immature samples inappropriate for source rock characterisation. A more realistic indication of the petroleum generative potential and oil expulsion efficiency of coaly source rocks can be gained from samples near the onset of expulsion. Alternatively, effective HI′ values (i.e. HIs near the onset of expulsion) can be estimated by translating the measured HIs of immature samples along the maturation pathway defined by the New Zealand (or other defined) Coal Band. Coaly source rocks comprise a continuum of coaly lithologies, including coals, shaly coals and coaly mudstones. Determination of the total genetic potential of coaly source rock sequences is best made using lithology-based samples near the onset of expulsion.  相似文献   

19.
Organochlorine pesticides (OCPs) are a class of toxic and harmful persistent organic pollutants widely found in environment. Hexachlorocyclohexane (HCHs) and DDTs are two of the most widely used OCPs (Qiu et al., 2004), so it is important to find out their compositional characteristics and sources in surface sediments. Guanghai Bay is located in the south of Guanghai Bay Industrial Park in Taishan City, Guangdong Province. It borders Huangmaohai to the east and Zhenhai Bay to the west, covering an area of about 236 square kilometers. In this study, surface sediments were collected at 16 sites in Guanghai Bay (Fig. 1). After the surface sediments were pretreated, GC‐MS was used to analyze OCPs. A total of 14 OCPs were detected and their content was shown in Table 1. The concentration of ΣOCPs ranged between 0.507～0.860ng·g‐1, with an average of 0.680 ng?g‐1. In general, the content of ΣOCPs was the highest at No. A12 site. The concentrations of these 14 detected OCPs ordered as dieldrin > epoxy heptachlor > P, P'‐DDD > γ‐HCH >endrin >aldrin > P, P'‐DDE >mirex >hexachlorobenzene >P, P'‐DDT > α‐HCH > δ‐HCH >β‐HCH > heptachlor.  相似文献   

20.
The distributions of hydrocarbons in sediment cores dated by 210Pb (1845–1977) from San Pedro and San Nicolas Basins in the Southern California Bight have been determined by gas Chromatographic and combined gas chromatographic-mass spectrometric analysis. The chromatograms of the hydrocarbons contain peaks of resolved alkanes and cycloalkanes, as well as an unresolved complex mixture which decrease in content with increasing depth in both of the cores. The concentrations of o,p' andp,p'-DDE are highest in the top 50 mm of the San Pedro core section. The 45–50 mm segment of this core was deposited in the 1945–1950 period when DDT (the precursor of DDE compounds) came into common use. The relatively high content of hydrocarbons and DDE in this core is attributable to the proximity of the site to the San Pedro Harbor which receives petroleum residues from shipping, sewage outfalls and industrial effluents. The presence of only traces of DDE throughout the San Nicolas core, and the low hydrocarbon content are explainable by the greater distance of this basin from anthropogenic inputs and probably a greater rate of degradation of deposited organic matter during bioturbation. δ13C, δ15N and electron-spin resonance analyses of kerogens and humic substances in these cores, indicate that most of this organic matter in these sediments is of a marine origin.  相似文献   

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