Hsueh-Yu Lu

Health risks for human intake of aquacultural fish: Arsenic bioaccumulation and contamination

Aquacultural tilapia (Oreochromis mossambicus L.) and shrimp (Penaeus monodon L.) from groundwater-cultured ponds in southwestern Taiwan were analyzed to estimate arsenic (As) bioaccumulation and the potential health risk to human intake. Most of aquacultural ponds exhibited higher arsenic than maximum allowed concentrations (50 μg L(-1)) in pond water of Taiwan. Arsenic levels in tilapia in Budai, Yichu and Beimen were 0.92 ± 0.52 μg g(-1), 0.93 ± 0.19 μg g(-1) and 0.76 ± 0.03 μg g(-1), respectively and in shrimp was 0.36 ± 0.01 μg g(-1) in Beimen. Total arsenic in tilapia is highly correlated (R(2) = 0.80) with total arsenic concentration of pond water. Total arsenic in fish showed high correlation with that in bone (R(2) = 0.98), head (R(2) = 0.97) and tissue (R(2) = 0.96). Organic arsenic species (DMA) was found higher relative to inorganic species of As(III) and As(V). The average percent contribution of inorganic arsenic to total arsenic in fish samples was 12.5% and ranged between 11.7 to 14.2%. Bioaccumulation factors (BAFs) for total arsenic in fish ranged from 10.3 to 22.1, whereas BAF for inorganic arsenic ranged from 1.33 to 2.82. The mean human health cancer risk associated with the ingestion of inorganic arsenic in the fish was estimated at 2.36 × 10(-4) ± 0.99 × 10(-4), which is over 200 times greater than a de Minimus cancer risk of 1 × 10(-6). The mean human health hazard quotient associated with ingesting inorganic arsenic in the fish was 1.22 ± 0.52, indicating that expected human exposure exceeds the reference dose for non-cancer health effects by 22%. These results suggest that the inhabitants in this region are being subjected to moderately elevated arsenic exposure through the consumption of tilapia and shrimp raised in aquaculture ponds.

Cretaceous fractionated I-type granitoids and metaluminous A-type granites in SE China: the Late Yanshanian post-orogenic magmatism

The Late Yanshanian Orogeny (130-90 Ma) encompasses an important Mesozoic magmatic event in the crustal evolution of SE China. Products of post-orogenic magmatism, widely distributed in the eastern part of Zhejiang and Fujian provinces known as the Southeast Coast Magmatic Belt (SCMB), are dominated by large amounts of slightly Nb and Ta depleted, high-K calc-alkaline granites (I-type) and small amounts of strongly Ba, Sr, Eu, Ti and P depleted, metaluminous granites (A-type). 40 Ar/ 39 Ar dating from amphiboles suggests that emplacement of A-type granites mostly postdates (94-90 Ma) the intrusion of voluminous I-type granitoids (110-99 Ma). Using the Al-in-amphibole geobarometer, I-type suites were estimated to have been emplaced at shallow depths (5-7 km). Along with the fact that A-type granites are phyric or miarolitic in texture, it can be concluded that all these post-orogenic suites in the SCMB belong to shallow intrusives. They have also undergone a rapid cooling (higher than 100°C/Ma at T > 300 °C) as indicated by the thermochronology of hornblende, biotite and K-feldspar; therefore, generation of A-type granites from I-type magmas through fractional crystallisation would be a difficult process. Alternatively, their geochemical characteristics are attributed to partial melting in the residual lower crust under an elevated geothermal environment. On the other hand, I-type magmas are considered to be middle-crust-derived melts largely modified with mantle-derived melts that had been depleted with Nb and Ta by earlier tectonic processes. Such a tectonic environment is explained by the underplating of basaltic magmas, most probably due to lithospheric delamination taking place at c. 110 Ma, which marks the beginning of the postorogenic episode in this area. Numerical modelling for a heat source provided by the underplating of basaltic magma supports such a proposition.

Simultaneous mountain building in the Taiwan orogenic belt

The obliquity of the arc-continent collision in Taiwan is thought to have produced a southward-propagating orogenic system starting as early as 8 Ma. We combine 62 new zircon fission-track ages with timing of rapid subsidence in the foreland basin to identify the timing of the onset of exhumation and orogenesis. The oldest completely reset zircon fission-track ages and the onset of rapid tectonic subsidence in both the northern and southern parts of the foreland basin are ca. 5–6 Ma. We propose that north-south rifting in the South China Sea created a north-trending continental margin before the collision rather than the commonly assumed northeast-trending margin. Consequently, both this north-trending continental margin and the Luzon arc of the Philippine Sea plate were subparallel, resulting in an initial collision that was simultaneous along strike.

Biogeochemical interactions among the arsenic, iron, humic substances, and microbes in mud volcanoes in southern Taiwan

Fluid and mud samples collected from Hsiaokunshui (HKS), Wushanting (WST), Yenshuikeng (YSK), Kunshuiping (KSP), Liyushan (LYS), and Sinyangnyuhu (SYNH) mud volcanoes of southwestern Taiwan were characterized for major ions, humic substances (HS) and trace elements concentrations. The relationship between the release of arsenic (As) and activities of sulfate-reducing bacteria has been assessed to understand relevant geochemical processes in the mud volcanoes. Arsenic (0.02-0.06 mg/L) and humic substances (4.13 × 10(-4) to 1.64 × 10(-3) mM) in the fluids of mud volcanoes showed a positive correlation (r = 0.99, p < 0.05) except in Liyushan mud volcano. Arsenic and iron in mud sediments formed two separate groups i) high As, but low Fe in HKS, WST, and SYNH; and ii) low As, but high Fe in the YSK, KSP, and LYS mud volcanoes. The Eh(S.H.E.) values of the mud volcano liquids were characterized by mild to strongly reducing conditions. The HKS, SYNH, and WST mud volcanoes (near the Chishan Fault) belongs to strong reducing environment (-33 to -116 mV), whereas the LYS, YSK, and KSP mud volcanoes located near the coastal plain are under mild reducing environment (-11 to 172 mV). At low Eh values mud volcanoes, saturation index (SI) values of poorly crystalline phases such as amorphous ferric hydroxide indicate understaturation, whereas saturation is reached in relatively high Eh(S.H.E.) values mud volcanoes. Arsenic contents in sediments are low, presumably due to its release to fluids (As/Fe ratio in YSK, KSP, and LYS sediment: 4.86 × 10(-4)-6.20 × 10(-4)). At low Eh(S.H.E.) values (mild to strong reducing environment), arsenic may co-precipitate with sulfides as a consequence of sulfate reduction (As/Fe ratios in WST, HKS, and SYNH sediments: 0.42-0.69).

Hydrochemistry and boron isotopes as natural tracers in the study of groundwaters from North Chianan Plain, Taiwan

In this paper, hydrochemistry and boron isotopes are successfully applied to elucidate hydrogeological processes by the use of natural tracers. The hydrochemical analysis identifies four end-members in the hydrochemical evolution of groundwater from the North Chianan plain groundwater district. A few groundwater contain extraordinary chlorine concentrations of up to 48,000 mg l−1. However, the hydrochemistry of groundwater only reveals that high saline water is a dominant factor in groundwater hydrochemistry. It is thought that these groundwater experienced precipitation of carbonates during seawater evaporation that did not involve the precipitation of gypsum. Boron isotopes are very efficient tracers in determining the source of salinisation. The boron isotopes reveal the results of mixing of evaporated seawater and water–sediment interaction. In general, the boron isotope ratio of the groundwater is controlled by a two-end-member mixing system, which is composed of evaporated seawater (isotopically heavy) and fresh surface water (isotopically light). Due to a long lagoonal period in the coastal plain, the groundwaters in the downstream area generally have high Cl/B ratios and relatively heavy boron isotope ratios while those in the upstream area are composed of low Cl/B and light boron isotopes. However, there is not a resolvable mixing trend between the Cl/B ratio and the isotopic composition of boron. It is probably obscured by a highly variable boron isotope ratio in fresh surface water and through fractionation associated with water–rock interaction. Both factors would decrease the boron isotope ratio but one effect cannot be distinguished from the other.

Study of diel hydrochemical variation in a volcanic watershed using principal component analysis: Tatun Volcano Group, North Taiwan

Heavy metal contamination commonly appears in mining areas and volcanic watersheds due to the acidic drainage water. Under the hydrochemical condition, the solar photocycle would result in changes of the water temperature, in photosynthesis and in iron photoreduction, which leads to substantial hydrochemical fluctuations, especially for heavy metals. It is important to consider the daily variations in water quality when developing a hydrochemical monitoring plan for an area with highly developed agriculture, such as the Tatun Volcano Group watershed area in this study. The results show that the water chemistry is highly complicated by both solar photocycles and hydrochemical fluctuations in the upstream area. Using principal component analysis, the contributions from the two factors can be successfully separated. During the daytime, the photocycle results in the formation of aluminum hydroxide, which can remove heavy metals from water. Consequently, the content of heavy metals, including As, Cu, Ni, Co and Ba, increases after sunset and can reach a maximum before sunrise, while Fe behaves inversely due to the photoreduction. The variation of As during a diel cycle can reach 97%. However, the content of most of the heavy metals during diel cycle is incomparable with those in the earlier studies due to the formation of aluminum hydroxide instead of iron hydroxide. The other significant factor, hydrochemical fluctuation, can explain the variation of major components in water including Cl, SO4. Rare earth elements (REEs) were also analyzed and can be an excellent natural tracer in this study. The distribution of REEs shows a depletion of light REEs and an even normalized concentration of middle and heavy REEs. It is theorized that the REEs in the water in this study derive mainly from the reservoir rock of geothermal water. In a hydrochemical monitoring plan, REEs can be an indicator for identifying an anthropogenic source.