Area Of Southwestern Taiwan Research Articles

Morphological traits and root anchorage ability of native pioneer tree species for reforestation of mudstone badlands

ABSTRACT Mudstone badlands occupy a large area in southwestern Taiwan. Mudstone soils with poor cementation property are particularly vulnerable to water erosion and landslides during rainy seasons. Broussonetia papyrifera, Hibiscus taiwanensis and Macaranga tanarius are major pioneer tree species occurring on mudstone badlands. Therefore, these species are beneficial for slope stabilization and forest restoration to control erosion and landslide. Nevertheless, information on their morphological traits and root biomechanical properties are lacking. In this research, root morphological traits of these species were inspected utilizing WinRHIZOPro Image Analysis System. Root anchorage ability and root tensile strength of 1-year-old B. papyrifera, H. taiwanensis and M. tanarius saplings were evaluated using uprooting testing and root tensile testing. The results show, compared to H. taiwanensis, B. papyrifera and M. tanarius plants had markedly greater root traits. Moreover, the root anchorage abilities of M. tanarius and B. papyrifer plants were notably higher than that of H. taiwanensis. In addition, root tensile strength of M. tanarius plants was markedly higher than those of B. papyrifera and H. taiwanensis plants. The results clearly demonstrate that M. tanarius outperforms B. papyrifera and H. taiwanensis, in these traits. Taken together, the priority for selecting these species for reforestation of mudstone badlands follows as: M. tanarius > B. papyrifera > H. taiwanensis. These results, together with the information on ecological succession following erosion and landslide, allow us to develop the reforestation plan and management strategy of mudstone badlands.

Seasonal variation and source apportionment of PM2.5-bound trace elements at a coastal area in southwestern Taiwan.

The aim of this study is to investigate the seasonal variations and source apportionment on atmospheric fine particulate matter (PM2.5) mass and associated trace element concentrations at a coastal area, in Chiayi County of southwestern Taiwan. Particle measurements were conducted in 2015. Twenty-three trace elements in PM2.5 were analyzed using inductively coupled plasma mass spectrometry (ICP-MS). Multiple approaches of the enrichment factor (EF) analysis and positive matrix fraction (PMF) model were used to identify potential sources of PM2.5-bound trace elements. Daily mean concentration of PM2.5 in cold season (25.41μgm-3) was higher than that in hot season (13.10μgm-3). The trace elements contributed 11.02 and 10.74% in total PM2.5 mass concentrations in cold season and hot season, respectively. The results of EF analysis confirmed that Sb, Mo, and Cd were the top three anthropogenic trace elements in the PM2.5; furthermore, carcinogenic elements (Cr, Ni, and As) and other trace elements (Na, K, V, Cu, Zn, Sr, Sn, Ba, and Pb) were attributable to anthropogenic emissions in both cold and hot seasons; however, highly enriched Li and Mn were observed only in cold season. The PMF model identified four main sources: iron and steel industry, soil and road dust, coal combustion, and traffic-related emission. Each of these sources has an annual mean contribution of 8.2, 27.5, 11.2, and 53.1%, respectively, to PM2.5. The relative dominance of each identified source varies with changing seasons. The highest contributions occurred in cold season for iron and steel industry (66.2%), in hot season for traffic-related emission (58.4%), soil and road dust (22.0%), and coal combustion (2.8%). These findings revealed that the PM2.5 mass concentration, PM2.5-bound trace element concentrations, and their contributions were various by seasons.

Late Quaternary mass-wasting records in the actively uplifting Pa-chang catchment, southwestern Taiwan

Although dominated by erosion over long term, the tectonically active mountains of Taiwan commonly contain thick landslide and debris-flow gravels capping hillslopes or forming alluvial terraces. These deposits and their associated landforms serve to study ancient mass-wasting histories and their controls on fluvial processes. This study focuses on the Pa-chang River draining the <2000m high Ali-shan area in southwestern Taiwan (current tectonic uplift: 5–8mmyr−1). Although small (catchment area: 83km2), the Pa-chang exhibits one of the largest alluvial terraces in Taiwan, which stretches from the outlet of the catchment for 9km along the river and comprises fluvial and debris-flow gravels up to 150m thick. Totally 55 radiocarbon dates have been obtained, tracing the mass-wasting records back to 14.8ka. The largest events, which created the studied major terraces, occurred in 10.0−11.3 and 8.7−9.4ka. These events are synchronous with the formation of some regionally largest alluvial terraces in Taiwan, and may have been triggered by the frequent heavy rains associated with the early Holocene East Asian summer-monsoon maximum. More mass-wasting events have been dated at ~5.4, ~1.9, 1.2−1.7, 0.7−0.9, ~0.6, and <0.3ka. The vast supply of sediment from the recorded mass-wasting events not only caused river aggradation but also regulated the subsequent incision by forming boulder armors. As a result, the bedrock incision in the upper part of the catchment has been negligible since the early Holocene debris-flow deposition. The incision rates increase to the downstream direction as the size and concentration of boulders reduce. Still, the 14.8ka-averaged bedrock incision rate (<4.5mmyr−1) at the catchment outlet is lower than the current uplift rate (6mmyr−1). At the same site, however, the bedrock incision rate is 23mmyr−1 averaged over the past 0.6ka. Even higher rates of incision (>50mmyr−1) are detected further downstream after the recent gravel mining. The fact that the obtained bedrock incision rates and patterns are decoupled with the tectonic uplift advises caution in using short-term erosion data to interpret the tectonics of the Taiwan's mountains.

Use of Arsenic-Induced Palmoplantar Hyperkeratosis and Skin Cancers to Predict Risk of Subsequent Internal Malignancy

Hyperpigmentation, hyperkeratoses, and Bowen's disease are hallmarks of chronic arsenic exposure. The association between arsenic-induced skin lesions and subsequent internal cancers is examined by using a community-based prospective study. The cohort was enrolled from an arseniasis-endemic area in southwestern Taiwan, where 2,447 residents participated in skin examinations during the late 1980s. The number of participants diagnosed with hyperpigmentation was 673; with hyperkeratosis, 243; and with skin cancer (Bowen's disease or non-melanoma skin cancer), 378. Newly diagnosed internal cancers were ascertained through linkage with National Cancer Registry profiles. Cox regression was performed to estimate hazard ratios with 95% confidence intervals for potential risk predictors. Compared with participants without skin lesions, patients affected with skin cancers had a significantly increased risk of lung cancer (hazard ratio = 4.64, 95% confidence interval: 2.92, 7.38) and urothelial carcinoma (hazard ratio = 2.02, 95% confidence interval: 1.23, 3.30) after adjustment for potential confounders and cumulative arsenic exposure. Hyperkeratosis is significantly associated with an increased lung cancer risk (hazard ratio = 2.76, 95% confidence interval: 1.35, 5.67). A significant interactive effect on lung cancer risk between hyperkeratosis and cigarette smoking was identified, which suggests that patients with hyperkeratosis who have been exposed to arsenic should cease smoking.

Centroid Fault-Plane Inversion in Three-Dimensional Velocity Structure Using Strong-Motion Records

The Chia-yi area in southwestern Taiwan is a region of relatively high seismicity. Frequent earthquakes of various magnitudes in the shallow crust provide valuable information for understanding the regional seismotectonic environment. In this study, we use strong-motion records from the 22 October 1999, ML 6.4 Chia-yi earthquake sequence to determine the focal mechanisms based on a criterion combin- ing the P-wave polarity and the cross correlations between recorded and synthetic waveforms. A recent 3D structural model for the study region is used, and to ensure the computational efficiency, a database is established for the Green's functions obtained by the finite-difference method. Optimal focal depths and fault-plane solu- tions are obtained through a grid-search scheme driven by the genetic algorithm to further improve the efficiency. We apply this approach to determine the focal mecha- nisms and centroid depths of the small and moderate events in the Chia-yi earthquake sequence. Results show dominant strike-slip and thrust mechanisms that are in good agreement with previous results based upon P-wave first-motion polarities and moment-tensor inversions. This highly automatic and efficient approach will enable the determination of focal depths and fault-plane solutions immediately following the occurrence of small- to moderate-sized earthquakes.

Electrical Resistivity Variations Before and After the Pingtung Earthquake in the Wushanting Mud Volcano Area in Southwestern Taiwan

The extensive eruption of fluid from the mud volcanoes in the Yanchao area of southwestern Taiwan reveals the activities of the active Chishan fault. A series of time-lapse resistivity imaging measurements were initially conducted in the Wushanting Natural Landscape Preservation Area in Yanchao to evaluate the relationship between resistivity change and fault activity. Resistivity measurements were conducted first along seven [Formula: see text] survey lines to build up the regional model for mud volcanoes. We then conducted consecutive hourly and daily measurements to evaluate the short-term resistivity variations. Monthly observation was initiated along two [Formula: see text] lines in July of 2006. On December 26, 2006, two successive earthquakes with magnitudes of 6.96 and 6.99 hit the town of Hengchun in Pingtung County, about [Formula: see text] southwest of the monitoring site. Before the Pingtung earthquake, the resistivity at the research site was less than [Formula: see text]. Two regions with relatively low resistivity were found at a depth greater than [Formula: see text] at the positions of the two mud volcano craters. The two low-resistivity regions indicate the locations of conduits for the mud fluid. The major changes of resistivity are located in the vadose zone between the surface and a depth of [Formula: see text]. After the Pingtung earthquake, the maximum resistivity increased in the vadose zone by [Formula: see text] and [Formula: see text] on survey lines D and E, respectively. In the zone, the estimated water content of D and E decreased by 7% and 10%, respectively, after the earthquake. We suggest that the decrease of resistivity in the vadose zone most likely reflects the decrease of water content, itself caused by the earthquake tremors’ increased emission of gas. Currently, we are continuing the resistivity-monitoring surveys and hope to provide more data to clarify the seasonal-variation patterns and to compare them with the previous findings.

Should Patients With Primary Upper Urinary Tract Cancer Receive Prophylactic Intravesical Chemotherapy After Nephroureterectomy?

We assessed the efficacy of prophylactic intravesical chemotherapy for primary upper urinary tract urothelial cancer after nephroureterectomy during long-term followup. From January 1985 to June 2007, 196 patients with primary upper urinary tract urothelial cancer were included in this study. Patients were divided into group 1-31 who received intravesical epirubicin instillation, group 2-27 who received intravesical mitomycin C instillation and group 3-138 who did not receive prophylactic instillation after nephroureterectomy. We compared the bladder tumor recurrence rate, number of recurrence episodes, time to first bladder tumor recurrence, tumor type, percent of patients with cystectomy and percent who died of urothelial cancer, and the recurrence-free survival rate. Of the 196 patients 73 had subsequent bladder recurrence at a mean followup of 55.6 months. There were no significant differences in recurrence type, mean number of bladder tumor recurrences, percent of patients with cystectomy and the cancer specific survival rate. The bladder recurrence rate was lower in group 1 and 2 than in group 3. Mean time to first bladder tumor recurrence was longer in groups 1 and 2. Kaplan-Meier curves of recurrence-free survival rates were significantly increased in groups 1 and 2. Intravesical instillation of epirubicin or mitomycin C appears to be well tolerated and effective for preventing bladder recurrence and prolonging time to first bladder recurrence. Patients should receive prophylactic intravesical chemotherapy after nephroureterectomy.

Risk of carotid atherosclerosis is associated with low serum paraoxonase (PON1) activity among arsenic exposed residents in Southwestern Taiwan

To understand whether human paraoxonase 1 (PON1) would modulate the risk for arsenic-related atherosclerosis, we studied 196 residents from an arseniasis-endemic area in Southwestern Taiwan and 291 age- and sex-matched residents from a nearby control area where arsenic exposure was found low. Carotid atherosclerosis was defined by a carotid artery intima-media wall thickness (IMT) of > 1.0 mm. Prevalence of carotid atherosclerosis was increased in the arseniasis-endemic area as compared to the control area after adjustment for conventional risk factors (OR = 2.20, p < 0.01). The prevalence was positively associated with cumulative arsenic exposure (mg/L-year) in a dose-dependent manner. Multiple logistic regression analysis showed that in the endemic group, low serum PON1 activity was an independent risk factor for atherosclerosis (OR = 4.18 low vs. high, p < 0.05). For those of low PON1 activity and high cumulative arsenic exposure, the odds ratio for the prevalence of atherosclerosis was further increased up to 5.68 ( p < 0.05). No significant association was found between atherosclerosis and four polymorphisms of the PON gene cluster (PON1 − 108C/T, PON1 Q192R, PON2 A148G, PON2 C311S). However, genetic frequencies of certain alleles including PON1 Q192, PON2 G148 and PON2 C311 were found increased in the endemic group as compared to the controls and a general Chinese population, indicating a possible survival selection in the endemic group after a long arsenic exposure history. Our results showed a significant joint effect between arsenic exposure and serum PON1 activity on carotid atherosclerosis, suggesting that subjects of low PON1 activity may be more susceptible to arsenic-related cardiovascular disease.

Associations between Arsenic in Drinking Water and Pterygium in Southwestern Taiwan

BackgroundPterygium is a fibrovascular growth of the bulbar conjunctiva and underlying subconjunctival tissue that may cause blindness. The mechanism of pterygium formation is not yet fully understood, but pterygium has some tumorlike features.ObjectivesThe objective of this study was to evaluate the association between arsenic exposure through drinking water and the occurrence of pterygium in southwestern Taiwan.MethodsWe recruited participants > 40 years of age from three villages in the arseniasis-endemic area in southwestern Taiwan (exposure villages) and four neighboring nonendemic villages (comparison villages). Each participant received an eye examination and a questionnaire interview. Photographs taken of both eyes were later graded by an ophthalmologist to determine pterygium status.ResultsWe included 223 participants from the exposure villages and 160 from the comparison villages. The prevalence of pterygium was higher in the exposure villages across all age groups in both sexes and increased with cumulative arsenic exposure. We found a significant association between cumulative arsenic exposure and the prevalence of pterygium. After adjusting for age, sex, working under sunlight, and working in sandy environments, we found that cumulative arsenic exposure of 0.1–15.0 mg/L-year and ≥ 15.1 mg/L-year were associated with increased risks of developing pterygium. The adjusted odds ratios were 2.04 [95% confidence interval (CI), 1.04–3.99] and 2.88 (95% CI, 1.42–5.83), respectively.ConclusionsChronic exposure to arsenic in drinking water was related to the occurrence of pterygium, and the association was still observed after adjusting for exposures to sunlight and sandy environments.

ECG Abnormality After Tap Implantation in Arsenic Exposure Area of South Western Taiwan

ECG Abnormality After Tap Implantation in Arsenic Exposure Area of South Western Taiwan

SNPs of GSTM1, T1, P1, epoxide hydrolase and DNA repair enzyme XRCC1 and risk of urinary transitional cell carcinoma in southwestern Taiwan

A hospital-based case-control study was conducted near a former black-foot disease (BFD)-endemic area in southwestern Taiwan to examine the possible risk factors and genetic susceptibility for urinary transitional cell carcinoma (TCC). A total of 221 patients with pathologically confirmed TCC and 223 age–sex-matched control subjects from urology outpatient clinics were recruited between 1998 and 2002. The results showed that residency in the BFD area and consumption of well water for more than 10 years was a strong factor on urinary cancer risk (odds ratio [OR],8.16, 95% confidence interval [CI],3.34–19.90, p < 0.0001). Dose response relationship between average arsenic concentration in well water and TCC risk was also observed. Cigarette smoking played a relatively minor role in urinary carcinogenesis in this study. The GSTP1 Ile105Val A → G polymorphism was significantly associated with cancer risk (A/G + G/G: OR = 0.60, 95%CI = 0.39–0.94, p = 0.02), and the effect of Val105 allele was largely confined to the subjects diagnosed earlier than 55 years old (A/G + G/G: OR,0.29; 95% CI, 0.09–0.87, p = 0.03). The results suggest that GSTP1 is a candidate for susceptibility locus and Ile105 allele may predispose individuals to early-onset urinary TCC. The GSTM1 null genotype was associated with tumors of high-invasiveness (OR,2.21; 95% CI, 1.34–4.73) as well as with early-onset TCC risk (OR,2.53; 95% CI, 0.97–6.59). Our preliminary results showed the XRCC1 Arg194Trp were associated with arsenic-related urinary TCC and the interaction between the genotype and the exposure was statistically significant. The modulating effect of the GSTM1, GSTT1, GSTP1 Ile105Val, EPHX Tyr113His and XRCC1 Arg280His on arsenic-related TCC risk was also suggestive. These observations implied that impaired metabolism of carcinogenic exposure as well as impaired DNA repair function play an important role in arsenic-related urinary transitional cell carcinogenesis.

How Creditable are Cancer Risk Estimates from the S.W. Taiwan Database for Arsenic in Drinking Water?

A database of cancer mortality and arsenic concentrations in village wells in an arseniasis-endemic area of southwestern Taiwan has been the predominant source of information for risk assessments of U.S. Environmental Protection Agency and two National Research Council reports on arsenic and drinking water. A limitation of the data, however, is that exposure is ecological, that is, cancer mortality cannot be matched with arsenic exposure on an individual basis, just grouped by village. The resultant potential for bias is examined by comparing dose-response analyses of villages divided into two groups, those with well concentrations in a narrow range and the remainder. The narrow range group suggests a flat or downward change in risk in the low dose range, whereas the other group indicates increasing risk. More disturbingly, however, the dose-response data are highly dispersed for both groups and the dose-response curve predicts background bladder/lung cancer levels much higher than a southwestern Taiwan comparison population. This may be due to a large variability between villages of the study area in bladder/lung cancer not directly attributable to arsenic. Including the comparison population in the dose-response analysis artificially anchors the dose-response curve at a background level inconsistent with the study population and likely just biases the slope factor upward.

Primary Intracerebral Hemorrhage Mortality Reduction After Installation of a Tap-Water Supply System in an Arseniasis-Endemic Area in Southwestern Taiwan

Mortality and morbidity of vascular diseases, including stroke, are known to be associated with chronic exposure to inorganic arsenic through drinking water. A tap-water supply system was implemented in the early 1960s in the blackfoot disease (BFD) endemic areas of Taiwan. The objective of this study was to examine whether mortality attributed to stroke decreased among residents living in the BFD-endemic areas after the curtailment of arsenic exposure. Further it was of interest to determine whether arsenic exposure was related to a specific type of stroke. Standardized mortality ratios (SMRs) for stroke were calculated for the BFD endemic area for the years 1971–2000. The study results show that mortality due to primary intracerebral hemorrhage (PIH) declined gradually after the improvement of drinking-water supply system by elimination of arsenic exposure through removal of artesian well water. Based on the reversibility and specificity criteria, the association between arsenic exposure and mortality due to PIH is likely to be causal.

Serum Dioxins and Dioxin-Like Polychlorinated Biphenyls in Pregnant Women Residing in a Contaminated Area

P-360 Introduction: We studied serum polychlorinated dibenzo-p-dioxin, dibenzofurans (PCDD/Fs) and dioxin-like polychlorinated biphenyls (PCBs) levels in pregnant women who live in the environmentally exposed area in southwestern Taiwan where a large pentachlorophenol (PCP) manufacturing plant were located and operated during 1965 – 1984. The present study was conducted to ascertain whether an increased body burden of dioxins existed in pregnant women living in an area contaminated by chemicals from this plant. Method: Twenty-eight pregnant subjects, 21–39 years of age and residing in the study area between with a mean dwelling time of 6.07 ± 6.11 years, were recruited. Concentrations of polychlorinated PCDD/Fs, and PCBs in serum of recruited residents were determined. The isotope dilution high resolution gas chromatography/high resolution mass spectrometry (HRGC/HRMS) method was used to quantitatively determine the PCDD/Fs and PCBs congeners. Results: Pregnant women residing in the study area > 3 years had significantly higher PCDD (7.48 versus 5.13 pg-toxic equivalents [TEQ]/g-lipid) and dioxin-like PCB (6.70 versus 3.74 pg-TEQ/g-lipid) values as compared to those residing 3 years. Observed results show that insulin had a positive trend TEQ, levels without statistical significance, nevertheless insulin sensitivity were significantly decreased with increasing levels of both PCB and total TEQ. Dioxin congeners with greater degrees of chlorine substitution (e.g., HpCDD/F and OCDD/F) partitioned to greater degrees in the subjects of this study as compared to subjects in the general Taiwanese population. Conclusion: Body burden may be increased in pregnant women living in the contaminated area. The relation of dioxin like PCB and total dioxin/PCB levels to insulin resistance is worth of noting because the later is related to diabetes occurrence.

Hypertension Incidence and Its Relation to Arsenic Ingestion: A 13-year Follow-up Study in Arseniasis Endemic Area of Southwestern Taiwan

Hypertension Incidence and Its Relation to Arsenic Ingestion: A 13-year Follow-up Study in Arseniasis Endemic Area of Southwestern Taiwan

Risk Assessment of Arsenic Exposure from Consumption of Cultured Milkfish, Chanos chanos (Forsskål), from the Arsenic-Contaminated Area in Southwestern Taiwan

Risk Assessment of Arsenic Exposure from Consumption of Cultured Milkfish, Chanos chanos (Forsskål), from the Arsenic-Contaminated Area in Southwestern Taiwan

Decreasing Trend in Renal Disease Mortality after Cessation from Arsenic Exposure in a Previous Arseniasis-Endemic Area in Southwestern Taiwan

Arsenic has been well documented as a major risk factor for blackfoot disease (BFD), a unique peripheral vascular disease that was endemic in the southwestern coast of Taiwan, where residents imbibed artesian well water containing excessive amounts of arsenic for more than 50 yr. Long-term arsenic exposure has also been reported to be associated with mortality attributed to renal disease. A tap-water supply system was implemented in the early 1960s in the BFD endemic areas. Artesian well water was no longer used for drinking and cooking after the mid-1970s. The objective of this study was to examine whether mortality attributed to arsenic-induced renal diseases decreased after the improvement of the drinking-water supply system through elimination of arsenic exposure from artesian well water. Standardized mortality ratios (SMRs) for renal diseases were calculated for the BFD endemic area for the years 1971–2000. Results show that mortality from renal disease declined gradually after improvement of the drinking-water supply system to eliminate arsenic from artesian well water. Based on the reversibility criterion, the association between arsenic exposure and mortality attributed to renal disease is likely to be positively correlated. This study was partly supported by a grant from the National Science Council, Executive Yuan, Taiwan (NSC-92-2320-B-037-046).

A PBTK/TD modeling‐based approach can assess arsenic bioaccumulation in farmed tilapia (Oreochromis mossambicus) and human health risks

A biologically based risk-assessment model of arsenic (As) exposure evaluated farmed tilapia (Orechromis mossambicus) and human health during tilapia consumption in an area of southwestern Taiwan where blackfoot disease (BFD) occurs. The risk assessment addressed exposures to city residents who lived in Taipei, Taichung, and Kaohsiung, as well as subsistence fishers living in the BFD area who consumed tilapia. The models implemented included a physiologically based toxicokinetic and toxicodynamic (PBTK/TD) model to account for As exposure and dose-response profiles in tilapia and a human health exposure/risk model that accounts for target lifetime risk (TR) and hazard quotient (HQ) for humans consuming farmed tilapia. Results demonstrated that 90th percentiles of TR ranged from 1.53 x 10(-8) to 1.62 x 10(-6) for city residents with farmed tilapia consumption rates of 0.41 to 1.37 g/d. The 90th percentiles ranged from 2.07 x 10(-6) to 7.89 x 10(-5) for subsistence fishers in the BFD area with farmed tilapia consumption rates of 16.80 to 59.15 g/d. All predicted 90th percentiles of HQ were less than 1 for city residents and subsistence fishers in the BFD area, indicating small contributions from farmed tilapia consumption. Critical variables included whole-fish body weight, water As content, and As level in tilapia muscle. Although bioaccumulation of As seems unlikely to result in toxicity to farmed tilapia and humans consuming tilapia, the theoretical human health risks in the BFD area are alarming, using a probabilistic risk-assessment model based on conservative assumptions.

Bladder cancer mortality reduction after installation of a tap-water supply system in an arsenious-endemic area in southwestern Taiwan

Arsenic has been well documented as the major risk factor for blackfoot disease (BFD), a unique peripheral vascular disease that was endemic in the southwestern coast of Taiwan, where residents had consumed high-arsenic artesian well water for more than 50 years. Long-term arsenic exposure has also been reported to be associated with bladder cancer mortality in a dose–response relationship. A tap water supply system was implemented in the early 1960s in the BFD endemic areas. Artesian well water was no longer used for drinking and cooking after the mid-1970s. The objective of this study is to examine whether bladder cancer mortality decreased after the improvement of the drinking water supply system through elimination of arsenic exposure from artesian well water. Standardized mortality ratios (SMRs) for bladder cancer were calculated for the BFD endemic area for the years 1971–2000. The study results show that mortality from bladder cancer declined gradually after the improvement of the drinking water supply system to eliminate arsenic exposure from artesian well water. Based on the reversibility criterion, this finding strengthened the likelihood of the observed association between arsenic exposure and bladder cancer being causal.

Lung cancer mortality reduction after installation of tap-water supply system in an arseniasis-endemic area in Southwestern Taiwan

Arsenic has been well documented as the major risk factor for blackfoot disease (BFD), a unique peripheral vascular disease (PVD) that was endemic in the Southwestern coast of Taiwan, where residents had used high-arsenic artesian well water for more than 50 years. Long-term arsenic exposure has also been reported to associated with lung cancer mortality in a dose-response relationship. A tap-water supply system was implemented in the early 1960s in the BFD-endemic areas. Artesian well water was no longer used for drinking and cooking after the mid-1970s. The objective of this study is to examine whether lung cancer mortality decreased after the improvement of drinking water supply system through elimination of arsenic exposure from artesian well water. Standardized mortality ratios (SMRs) for lung cancer were calculated for the BFD-endemic area for the years 1971–2000. The study results show that mortality from lung cancer declined gradually after the improvement of drinking water supply system to eliminate arsenic exposure from artesian well water. Based on the reversibility criterion, the association between arsenic exposure and lung cancer mortality is likely to be causal.