Polychlorinated biphenyls in freshwater fish from the Zagreb area

The aim of this study was to determine the levels of six polychlorinated biphenyls (referred to as PCB-28, PCB-52, PCB-101, PCB-138, PCB-153 and PCB-180, according to the IUPAC) in freshwater fish from the Zagreb area. A total of 216 samples was collected from five sites: from the Sava River upstream of Zagreb, in Zagreb, and downstream of Zagreb, from Lake Jarun, and from five fishponds from the Zagreb surroundings. Samples from all five sites contained polychlorinated biphenyls (PCBs). The maximal levels found in individual samples ranged between 20 microg kg(-1) and 50 microg kg(-1) depending on the congener. However, the total level of all examined congeners was far below the maximal allowed level of 2.0 mg kg(-1) ww, set by Croatian authorities for total PCBs.     

Determination of Organochlorine Pesticide Residues in Freshwater Fish Species in Punjab,India

The levels of organochlorine pesticides residues were determined in five freshwater fish species in Punjab State, India. These species were selected in view of their importance to local human fish consumer. DDTs were the predominant organochlorine contaminants in all species with pp DDT and pp DDE as the main pollutants. Other organochlorines, such as HCH isomers and dieldrin were also found at lower levels in fish species. The α-HCH was the dominant isomer of HCH in all fish species followed by γ-, β- and δ-HCH. The residues of aldrin, chlordane, heptachlor and endosulphan were not detected in any fish sample. The levels of organochlorines detected in present study were below the tolerance limits recommended at National and International standards.     

Relations Between Land Use and Organochlorine Pesticides,PCBs, and Semi-Volatile Organic Compounds in Streambed Sediment and Fish on the Island of Oahu,Hawaii

Bed-sediment and/or fish samples were collected from 27 sites around the island of Oahu (representing urban, agricultural, mixed, and forested land use) to determine the occurrence and distribution of hydrophobic organic compounds including organochlorine pesticides, polychlorinated biphenyls (PCBs), and semi-volatile organic compounds (SVOCs). Of the 28 organochlorine compounds analyzed in the fish, 14 were detected during this study. Nineteen of the 31 organochlorine compounds and 40 of the 65 SVOCs were detected in the sediment. Urban sites had the highest number of detections and tended to have the highest concentrations of pesticides. Chlordane compounds were the most frequently detected constituents at urban sites, followed by dieldrin, polycyclic aromatic hydrocarbons (PAHs), and DDT compounds. PAHs were the most frequently detected constituents in watersheds with mixed (urban and agricultural) land use. The only pesticides detected at agricultural sites were DDT and its degradation products, DDD and DDE. No pesticides or PCBs were detected at the forested sites, but a few ubiquitous SVOCs were found in sediments at some forested sites. In general, concentrations of the most frequently detected pesticides were higher in fish than in sediment. Following a trend that has been observed elsewhere in the nation, concentrations of most organochlorine pesticides and PCBs are decreasing in Hawaii.     

Organochlorine pesticides in wolves from Galicia

Levels of seven organochlorine pesticides (heptachlorepoxide, dieldrin, endrin, p,p'-DDE, o-p'-DDT, p,p'-DDT, and methoxychlor) and DDE/DDT ratios were determined in spleen, liver, muscle, kidney and suprarenal from 12 wolves from three provinces of Galicia (eight male and four female). Analysis was carried out by GC-ECD. Heptachlorepoxide was in found only 25% of samples, while p,p'-DDE was the most dominant of the organochlorine compounds analyzed. DDE/DDT ratios higher than 1 were found in liver and muscle.     

1982至2002年北京地区人乳中有机氯农药水平监测

目的 了解城区正常居民人乳中有机氯农药双对氯苯基三氯乙烷(滴滴涕,DDT)、六氯环己烷(六六六,BHC)和六氯苯(HCB)的基础水平,并通过连续监测,对我国1983年停用DDT、BHC农药的效果进行综合评价。方法 采集1982至2002年在北京市城区至少居住5年以上,并且不从事有机氯农药生产与销售,家庭成员也不从事该项工作,且采集的样品为产后1周至4个月内的产妇乳汁。采用我国生物监测统一方法进行测定。结果 1982年北京市城区人乳中总DDT农药含量为6．45mg／kg,总BHC农药含量为6．97mg／kg。自1983年我国政府停用该两种农药以来,人乳中的含量出现了明显下降。以世界粮农组织(FAO)／世界卫生组织(WHO)的标准计算,北京市1998年以后出生的婴儿总DDT平均摄入量为11μg／kg,β-。BHC平均摄入量为6μg／kg,分别小于WHO和日本厚生省规定的每日最高可受摄入量。结论 北京市1998年以后出生的婴儿由母乳中摄入的DDT、BHC农药含量已处于安全水平,表明我国控制DDT、BHC农药的使用取得了很好的成效。     

Continuous surveillance of organochlorine pesticides in human milk from 1983 to 1998 in Beijing, China

A study was carried out to study the accumulative levels and dynamic changes of organochlorine pesticides in human milk in Beijing from 1982 to 1998, and the effect of prohibition and restriction on the use of DDT and BHC (666) in China in 1983. The milk samples were collected from women during the lactation period in four districts of Beijing from 1982 to 1998, in 1991, 1993 and 1998, respectively. The contents of DDT and BHC in human milk were determined according to the standard method of biology-monitoring of PR China. The average fat content of human milk was about 3% from 1982-1998 in Beijing. The average concentration of pp-DDT and op-DDT in 1985 was less than 0.10 mg/kg and remained so until 1998. The average concentration of pp'-DDT decreased from 1.80 mg/kg in 1982 to 0.24 mg/kg in 1998 and that of pp-DDE descended from 5.87 mg/kg to 1.72 mg/kg and the total concentration of DDT dropped from 7.71 mg/kg to 2.04 mg/kg. Since prohibition of organochlorine pesticides 1983, the average concentration of beta-BHC and total BHC fell respectively from 9.66 mg/kg and 10.1 mg/kg in 1983 to 1.18 mg/kg in 1998. However, the accumulative concentration of DDT and BHC was much higher than that of some foreign countries. Therefore, it was important and necessary to monitor organochlorine compounds in human milk continuously.     

Organochlorine pesticide residues in water and sediments from the Ovens and King Rivers,North-East Victoria,Australia

Water and sediment samples were taken from five sites on the Ovens and King Rivers (Australia) and analyzed for organochlorine pesticides residues. Residue concentrations were also determined in water samples taken at two hourly intervals during a 32-h storm flow event on the Ovens river. Residues detected in the rivers were most likely transported from surrounding land and upstream sources. The concentrations of DDE, DDT, and dieldrin residues were not different in different depositional areas, although increased proportions of DDD were found in sediments in the quiescent areas of the rivers. More than 70% of the dieldrin residues were found in the unsettled sediment fraction. Changes in flow during the storm event had a marked effect on the residues detected in the water column. DDT was present in largest amounts, which was most likely due to its association with nonfilterable organic matter.     

威海市农产品及人乳中有机氯农药残留量的调查

目的 了解有机氯农药的环境污染水平和人体蓄积水平。方法 检测了威海市主要农产品（小麦、玉米、花生、苹果）中的有机氯农药残留量和人乳中有机氯农药蓄积水平。结果 所调查的4种农产品中残留有机氯农药的检出率在0－60.0%,多数属于痕量检出,其最大检出值为国家卫生标准的1／28－1／5。人乳中666总量中位数为2.29mg/kg（以乳脂汁）;DDT总量中位数为2033mg/kg（以乳脂计）。分别降为全国80年代初期水平的1／3和1／5。结论 威海市有机氯农药的环境污染已基本消除,母乳中残留的有机氯农药对下一代健康影响不容忽视。     

Use and impact of pesticides in Egypt

Pesticides used in Egypt are of different types such as organochlorine, organophosphorus, carbamates, ureas, anilides and pyrethroid. The four general categories of these pesticides are insecticides, fungicides, herbicides and bactericides. Organophosphorus insecticides are of great significance in pest control and increasingly used instead of organochlorine insecticides. Organophosphorus insecticides represent more than 80% of total insecticides used during 1995. Fungicides account for 65.5% of pesticides used in Egypt during the period 1994-95 and agricultural use constitutes the majority of applications. Herbicides account for less than 4% of the pesticides used during 1995 in Egypt. The residue levels of some organochlorine insecticides (OCIs) and polychlorinated biphenyls (PCBs) in water, sediment and fish samples collected from the River Nile, lakes, drains and irrigation canals were determined. The highest concentration of OCI was found in samples collected from site located at north of Aswan (2.2 mug/l). Generally, the levels of OCI in River Nile water are still within safety margins, compared to the permissible limits for drinking waters. Also, the results demonstrated that fish samples from the River Nile and main lakes are contaminated with low levels of OCI and PCBs and there is no public health risk from fish consumption.     

Organochlorine Pesticide Content of Human Adipose Tissue in Karachi

The organochlorine group of pesticides, because of their persistence in tissue, are suspected of having adverse effects on human health. The present article is a report on the concentration of seven organochlorine compounds in the stored fat of 60 subjects from the Karachi, Pakistan, area who gave no history of occupational exposure to pesticides. The results indicate that people living in this city are heavily exposed to DDT, moderately exposed to benzene hexachloride (BHC), and only lightly exposed to aldrin/dieldrin. The extent of the exposure to pesticides was not related to the age, sex, type of material, residential location of subjects, or period during which samples were collected. The higher mean concentration of dichlorodiphenyl dichlo- roethane (DDD) in the postmortem specimens is probably due to microbial metabolism of DDT under anaerobic conditions after death.     

Perinatal metabolism of dichlorodiphenyldichloroethylene in Nicaraguan mothers.

Umbilical cord and venous blood samples were collected at the time of delivery from 52 mothers living in urban and rural areas of the Atoya River basin, Nicaragua. In a subsample of 24 mothers that delivered by Cesarean section, abdominal adipose tissue samples were also collected, as was breast milk later in lactation. Cord and venous blood sera were analyzed for 13 organochlorine pesticides: 1,1,1-trichloro-2,2-bis(4-chlorophenyl)ethane (pp'-DDT); 1,1-dichloro-2,2-bis(p-chlorophenyl)ethylene (pp'-DDE); pp'-dichlorophenyldichlorodiene (pp'-DDD); alpha-hexachlorocyclohexane (alpha-HCH); beta-hexachlorocyclohexane (beta-HCH); gamma-hexachlorocyclohexane (gamma-HCH); delta-hexachlorocyclohexane (delta-HCH); toxaphene; dieldrin; endrin; aldrin; heptachlor; and heptachlor epoxide. In venous blood only pp'-DDE (100% of samples), pp'-DDT (1.92%), dieldrin (15.38%), heptachlor (15.38%), gamma-HCH (7.69%), beta-HCH (11.53%), and delta-HCH (1.92%) were found, whereas in cord blood only pp'-DDE (100%), pp'-DDT (3.84%), dieldrin (19.23%), and heptachlor (9.16%), were found. The persistent DDT metabolite pp'-DDE, present in all samples of blood serum, adipose tissue, and breast milk, was studied in relation to maternal characteristics such as body mass index (BMI), age, lactation experience, and fetal pesticide acquisition. Mean venous (7.12 microg/g) and cord (6.39 microg/g) pp'-DDE concentrations were not significantly different but were significantly correlated. pp'-DDE in maternal adipose tissue was positively correlated with pp'-DDE in cord blood (P=0.0001) and breast milk (P<0.0001) and marginally correlated with changes in BMI (r=-0.03088; P=0.06). There was a higher proportion of samples (58%) with a greater concentration of DDE in venous than in cord blood. Although DDE accumulation may be less during fetal development than during breast feeding, exposure during embryogenesis may be more important than during the postnatal period.     

Studies on Organochlorine Pesticide Residue in Fishes from the Densu River Basin, Ghana

The study was carried out to determine the levels of organochlorine pesticide residue in five fish species Chrysichthys nigrodigitatus, Hepsetus odoe, Tilapia zilli, Heterotis niloticus and Oreochromis niloticus from the Densu river basin (Weija) in Ghana. The fishes sampled from the Weija fish landing site were selected on the basis of their importance to local human fish consumption. The detectable organochlorine pesticides were γ-Hexachlorocyclohexane (HCH), δ-Hexachlorocyclohexane, aldrin and dieldrin. Others investigated were alpha endosulfan, endosulfan sulfate, p,p’-DDT and its metabolite p,p’-DDE, endrin and its metabolite endrin aldehyde and endrin ketone. The total contamination levels of the individual fishes varied in the decreasing order of 9.19 ng g^?1 (O. niloticus), 4.16 ng g^?1 (T. zilli), 3.69 ng g^?1 (C. nigrodigitatus), 3.68 ng g^?1 (H. odoe) and 3.09 ng g^?1 (H. niloticus). The highest organochlorine pesticide residue recorded in the study was alpha-endosulfan while dieldrin was the least pesticide observed. Analysis of variance indicated significant statistical differences for most organochlorine pesticide residues in the samples. The levels of organochlorine pesticides found in fish samples in the study were below maximum residue limit for food safety stipulated by EU, US FDA, FAO, Italy and Australia and thus safe for human consumption.     

Pesticide residues in table-ready foods in Tanzania

This study investigated the presence of pesticide residues in table-ready foods in Tanzania. One-hundred-and-eighty nine samples of 11 widely used foods at table ready stage were analysed using US FDA multi-residue methods. Pesticide residues were detected in 29% of all samples analysed. The spread of contamination in individual foods was: spinach 72.7%, rice 50%, beef meat 42.1%, stiff porridge 8.6%, and beans 6.7%. After allocating Non-detects levels a half value of Method Detection Limit i.e., (MDL)/2, the mean concentrations of the pesticide residues in the foods were; In spinach: g-HCH 0.08 microg/kg; DDT 2.89 microg/kg; Chlorpyrifos 0.02 microg/kg. In rice: g-HCH 0.08 microg/kg; DDT 1.70 microg/kg; and Chlorpyrifos 0.02 microg/kg. In beef meat: g-HCH 0.14 microg/kg; DDT 0.76 microg/kg. In stiff porridge: g-HCH 0.06 microg/kg; and DDT 0.30 microg/kg. In beans: g-HCH 0.04 microg/kg; and DDT 0.13 microg/kg. In fish variety: g-HCH 0.05 microg/kg. Converted into consumer Average Daily Doses, these concentrations were within ADI/ PTDI levels set by CODEX and, therefore, posed no significant health risk. However, the presence of pp-DDT in many samples indicates a possible recent contamination of food raw materials with DDT. A more effective pesticides control system should be put in place before lifting the ban on DDT for restricted uses in vector control programs in Tanzania.     

Organochlorine compounds in bed sediment and fish tissue in the South Platte River Basin, USA, 1992–1993

Bed-sediment and fish-tissue samples were collected in the South Platte River Basin to determine the occurrence and distribution of organochlorine compounds in the basin. During August–November 1992 and August 1993, bed sediment (23 sites) and fish tissue (subset of 19 sites) were sampled and analyzed for 32 organochlorine compounds in bed sediment and 27 compounds in fish tissue. More types of organochlorine compounds were detected in fish tissue than in bed sediment. Total DDT, p,p′-DDE, o,p′-DDE, p,p′-DDD, total PCB, Dacthal^®, dieldrin, cis-chlordane, cis-nonachlor, trans-nonachlor, and p,p′-DDT were detected in fish tissue at >25% of the sites; p,p′-DDE, total DDT, cis-chlordane, and trans-chlordane were detected in bed sediment at >25% of the sites. Organochlorine concentrations in bed sediment and fish tissue were related to land-use settings. Few organochlorine compounds were detected at minimally impacted sites located in rangeland, forest, and built-up land-use settings. Chlordane-related compounds and p,p′-methoxychlor in bed sediment and fish tissue, endrin in fish tissue, and endosulfan I in bed sediment were associated with urban and mixed (urban and agricultural) sites. Dacthal^® in bed sediment and fish tissue was associated with agricultural sites. The compounds HCB, γ-HCH, PCA, and toxaphene were detected only at mixed land-use sites. Although DDT and DDT-metabolites, dieldrin, and total PCB were detected in urban, mixed, and agricultural land-use settings, highest mean concentrations were detected at mixed land-use sites. Mixed land-use sites had the greatest number of organochlorine compounds detected in fish tissue, whereas urban and mixed sites had the greatest number of organochlorine compounds detected in bed sediment. Measuring concentrations of organochlorine compounds in bed sediment and fish tissue at the same site offers a more complete picture of the persistence of organochlorine compounds in the environment and their relation to land-use settings.     

Geographic variation of chlorinated hydrocarbons in burbot (Lota lota) from remote Lakes and Rivers in Canada

The variation in levels of polychlorinated biphenyls (PCBs), chlorobenzenes and chlorinated pesticides was studied in burbot (Lota lota) from eight remote locations along a northwesterly transect from northwestern Ontario to the Mackenzie River delta in Canada. Significant declines in concentrations of PCB congeners, DDT isomers (DDT), lindane, dieldrin, and mirex in burbot liver were found with increasing north latitude. Mean PCB concentrations ranged from 1,290 ng/g (lipid wt) at Lake 625, a remote lake in northwestern Ontario, to 301 ng/g in samples from the Mackenzie River at Arctic Red River, N.W.T. No significant differences in mean concentrations of toxaphene, -HCH, tri- and tetrachlorobiphenyls were observed between southern and northern sampling sites. Toxaphene was the predominant organochlorine residue in northern fish samples averaging 1,400 ng/g (lipid wt) at the three most northerly sites and 1,723 ng/g at Lake 625. Airborne contamination was the only likely source of organochlorine s for most of the locations surveyed. The results were consistent with the hypothesis that inputs of semi-volatile organochlorines to northern aquatic ecosystems decrease with increasing north latitude and distance from North American sources.     

Predicting chemical contaminants in freshwater sediments through the use of historical biochemical endpoints in resident fish species

Previous studies in Bayou Bartholomew, Arkansas, USA, indicated significant relationships between the individual health of fish sampled from 13 sites and specific biochemical responses. Evaluation of several biochemical endpoints in 1994 indicated the bioavailable occurrence of either polychlorinated biphenyl (PCB) congeners or metals. To evaluate this possibility, in December 2000, sediments were collected at four sites on Bayou Bartholomew, where fish, collected in July 1994, had previously demonstrated the highest hepatic cytochrome P4501A (CYP1A) and heme oxygenase (HO) expression. Samples were analyzed for 89 PCB congeners, 18 organochlorine pesticides, and 25 metals. Total PCB concentrations ranged from 6.5 to 704 ng/g dry weight. Although several PCB congeners were observed, 81, 87, 99, 114, and 153 represented up to 33, 22, 29, 92, and 55% of the sum of PCBs from the four sites, respectively. Total organochlorine pesticide concentrations ranged from undetectable to 53.2 ng/g dry weight. Lindane, heptachlor, dachtal, dieldrin, hexachlorobenzene, dichlorodiphenyltrichloroethane (DDT), dichlorodiphenyl ethane (DDE), and dichlorodiphenyl dichloroethane (DDD) isomers were detected in most samples. Detected organophosphate pesticides included malathion, chlorpyrifos, and dimethoate. Both p,p'-DDE and p,p'-DDD were the most predominant of the pesticides measured (0.5-14.1 and 0.7-58.5 ng/g dry wt). All metal concentrations analyzed were below sediment quality guideline values. Metals exceeding national average concentrations were cobalt (2 of 4 [2/4] sites), copper (1/4), molybdenum (4/4), antimony (3/4), selenium (4/4), tin (4/4), and zinc (1/4). These results were consistent with PCBs being causative agents for the biochemical and adverse individual responses observed in fish sampled from this waterway.     

Health Risks Associated With Pesticide Residues in Sediments, Fish, and Plants From the Ouémé Valley in the Republic of Bénin

To determine possible human and environmental health risks, organochlorine pesticide residues were determined in vegetables grown in floodplains along the Ouémé River near Lowé in Bénin. Testing of vegetables found 13 pesticides with ΣDDT, α-endosulfan, Σdrin, and lindane being most important. The same pesticides were also detected in plants eaten by bovine cattle, sheep, and herbivorous fish. Human pesticide intake by vegetable consumption was compared with tolerable daily intake (TDI) values reported by the World Health Organization. Pesticide intake by fish consumption was estimated from residue levels in whole fish collected from the Ouémé River in 2004 and reported earlier. Fish consumption does not pose a risk for human health, but consuming vegetables that contain pesticide residues may lead to exceedance of TDI values. Based on these findings, concerns are warranted, and more work is needed to understand the full exposure profile for the local population.     

Predictors of adipose tissue concentrations of organochlorine pesticides in a general Danish population

Organochlorine pesticides are ubiquitously present in the environment and suspected of carcinogenic, neurological and immunological effects. Our objective was to identify determinants of adipose tissue levels of organochlorine pesticides experienced by a general Danish population. Adipose tissue was collected upon enrolment of 245 randomly selected persons from a prospective cohort of 57,053 persons enrolled between 1993 and 1997. We examined geography, gender, age, lactation, body mass index (BMI) and intake of nine dietary groups and tap water drinks, as potential determinants of dichlorodiphenyltrichloroethane (DDT), dichlorodiphenyldichloroethylene, hexachlorocyclohexane, dieldrin, hexachlorobenzene, cis-nonachlor, trans-nonachlor and oxychlordane. Living in Copenhagen city and age at enrolment showed positive associations with all compounds. BMI was positively associated with all compounds except cis-nonachlor. Fatty-fish consumption showed positive associations with cis-nonachlor, trans-nonachlor, DDT and dieldrin and fruit and vegetables were inversely associated with dieldrin. Determinant estimates of trans-nonachlor were similar to estimates of total chlordanes while cis-nonachlor and oxychlordane seemed to differ. This is one of the first studies of organochlorine pesticides predictors in adipose tissue and contributes to the ongoing debate about exposure sources of these compounds. Single determinants varied among the individual compounds, even within related chlordane residues, suggesting that organochlorine pesticides should not be treated as a homogenous group.     

Breast Milk Excretion Kinetic of β-HCH, pp′DDE and pp′DDT

Breast milk is considered the most important route in the elimination of deposited organochlorine pesticides in a mother’s body. The equilibrium of organochlorine pesticides in the human body considers the elements of internal transport processes, the equilibrium pattern between pesticides and tissue fat contents, and the mobilization of lipids and lipoproteins among body parts. The aim of this study was to determine organochlorine pesticide levels in breast milk samples from the 4th to the 30th day of lactation and the trend in their concentration time so as to forecast the time tendency of residue levels and the pesticide excretion pattern. Milk samples were taken from forty participants and analyzed by GLC-ECD. The organochlorine pesticide residues determined in the breast milk samples during lactation decreased: β-HCH from 0.095 to 0.066 mg/kg, pp′DDE from 1.807 to 1.423 mg/kg and pp′DDT from 0.528 to 0.405 mg/kg, at the characteristic rate for each compound. The obtained results compared with the calculated fits of forecasts were parallel and did not exhibit significant differences. The newborn baby exposed during lactation had organochlorine pesticide residues whose levels decreased permanently. The levels depended not only on the breast milk nutrition, but also on the total environmental exposures which included air pollution as a significant contamination source.     

Partition distribution of insecticides as a critical factor affecting their rates of absorption from water and relative toxicities to fish

Loaches,Misgurnus anguillicaudatus (Cantor), a common fish in Taiwan, were treated with DDT, dieldrin, and monocrotophos by continuous exposure in aqueous solutions (or suspensions) and by injection. DDT and dieldrin were 150 and 220 times more toxic, respectively, than monocrotophos, to the fish exposed in aqueous solutions (24-hr LC₅₀), but only 1/9 and 1/4 as toxic as monocrotophos by injection (24-hr LD₅₀). Results of GLC analyses indicate that, at the end of 24-hr exposure, 96.5% of DDT, 92.7% of dieldrin, and 14.3% of monocrotophos were absorbed by loaches from aqueous solutions. The initial rates of absorption for DDT and dieldrin were about 10 to 20 times faster than that for monocrotophos. The large differences in relative toxicity may be due to partition distribution which in turn caused differences in absorption, as DDT and dieldrin are lipophilic and monocrotophos is hydrophilic. Statistical analysis of the relationship between fish toxicities and partition coefficients supports the present finding. The coefficient of correlation is 0.70 between partition coefficients (benzene/water) and toxicities to fish (rainbow trout) of 12 organophosphorus insecticides, 0.74 between coefficients and corrected fish toxicities, and 0.96 between partition coefficients and corrected fish toxicities for organophosphates only. Results of analyses are significant at <1% probability level. Similar correlation was also obtained between partition coefficients for hexane/water and toxicities of 8 organophosphorus and 5 organochlorine insecticides to rainbow trout.This investigation was supported by grants from the Joint Commission on Rural Reconstruction, Republic of China.For reprints, please write to the Plant Protection Center, Taiwan, Taichung Hsien, Taiwan 431, Republic of China.This paper constitutes partial fulfillment of requirements for the M.S. degree of the senior author at the National Taiwan University.