Screen for low-arsenic-risk rice varieties based on environment-genotype interactions by using GGE analysis.

Arsenic (As) accumulation in rice is a global health concern that has received increased attention in recent years. In this study, 12 rice genotypes were cultivated at four As-contaminated paddy sites in Taiwan. According to the different crop seasons and As levels in the soil, the sites were further divided into 18 environmental conditions. For As in soils, results showed that 67% of the studied environments were likely to represent As contamination. For As in rice, the mean total As concentration in brown rice grains ranged from 0.17 to 0.45 mg kg-1. The analysis of variance for the environment effect indicated that grain As concentration was mainly affected by the environmental conditions, suggesting that there was a remarkable degree of variation across the trial environments. According to the combination of the GGE biplot and cumulative distribution function of order statistics (CDFOS) analysis, five genotypes-TCS17, TCS10, TT30, KH139, and TC192-were regarded as stable, low-risk genotypes because the probability of grain As concentration exceeding the maximum permissible concentration (MPC) was lower for these genotypes across all environmental conditions. Particularly, TCS17 was recommended to be the safest rice genotype. Thus, grain As levels in the selected genotypes were applied to assess the health risk to Taiwanese residents associated with As exposure through rice consumption. Results showed that the upper 75th percentile values of the hazard quotient were all less than unity. This suggested that the health risk associated with consuming the selected rice genotypes was acceptable for most of the residents. The methodology developed here would be applicable to screen for stable, low-As-risk rice genotypes across multiple field environments in other regions or countries.

Modeling Alleviative Effects of Ca, Mg, and K on Cu-Induced Oxidative Stress in Grapevine Roots Grown Hydroponically.

The aim of this study was to determine the pattern of alleviation effects of calcium (Ca), magnesium (Mg), and potassium (K) on copper (Cu)-induced oxidative toxicity in grapevine roots. Root growth, Cu and cation accumulation, reactive oxygen species (ROS) production, and antioxidant activities were examined in grapevine roots grown in nutrient solutions. The experimental setting was divided into three sets; each set contained a check (Hoagland solution only) and four treatments of simultaneous exposure to 15 µM Cu with four cation levels (i.e., Ca set: 0.5, 2.5, 5, and 10 mM Ca; Mg set: 0.2, 2, 4, and 8 mM Mg; K set: 0.6, 2.4, 4.8, and 9.6 mM K). A damage assessment model (DAM)-based approach was then developed to construct the dose-effect relationship between cation levels and the alleviation effects on Cu-induced oxidative stress. Model parameterization was performed by fitting the model to the experimental data using a nonlinear regression estimation. All data were analyzed by a one-way analysis of variance (ANOVA), followed by multiple comparisons using the least significant difference (LSD) test. The results showed that significant inhibitory effects on the elongation of roots occurred in grapevine roots treated with 15 µM Cu. The addition of Ca and Mg significantly mitigated phytotoxicity in root growth, whereas no significant effect of K treatment on root growth was found. With respect to oxidative stress, ROS and malondialdehyde (MDA) contents, as well as antioxidant (superoxide dismutase (SOD), catalase (CAT), and ascorbate peroxidase (APX)) activities, were stimulated in the roots after exposure to 15 µM Cu for three days. Moreover, H2O2 levels decreased significantly as Ca, Mg, and K concentrations increased, indicating that the coexistence of these cations effectively alleviated Cu-induced oxidative stress; however, alleviative effects were not observed in the assessment of the MDA content and antioxidant enzyme activities. Based on the DAM, an exponential decay equation was developed and successfully applied to characterize the alleviative effects of Ca, Mg, and K on the H2O2 content induced by Cu in the roots. In addition, compared with Mg and K, Ca was the most effective cation in the alleviation of Cu-induced ROS. Based on the results, it could be concluded that Cu inhibited root growth and Ca and Mg absorption in grapevines, and stimulated the production of ROS, lipid peroxidation, and antioxidant enzymes. Furthermore, the alleviation effects of cations on Cu-induced ROS were well described by the DAM-based approach developed in the present study.

Cadmium in rice grains from a field trial in relation to model parameters of Cd-toxicity and -absorption in rice seedlings.

Selecting rice varieties that absorb less Cd from soil will reduce human health risks posed by Cd through rice consumption. Nine rice cultivars that are commonly grown in Taiwan were used for investigating genotypic differences in Cd tolerance and absorption. Hydroponic testing with Cd treatments of 5, 10, and 50 µM CdCl2 for 7-day exposure was conducted for the cultivars. The reductions in plant growth by Cd treatments were fitted to a dose-response curve; the modeling parameters, that is, the effective Cd concentration resulting in 50% reduction (EC50), were obtained. The Cd concentrations in plant were expressed by a Michaelis-Menten kinetic model and the uptake rate parameters (M/k) were obtained. A field experiment was also conducted in farmland with Cd ~0.2 mg kg-1 in soil. For the rice cultivars used in hydroponics, Cd distributions and physiological traits (CAT, H2O2, and MDA) in seedlings were related to their tolerances to Cd toxicity. Modeling parameters, EC50 and M/k, correspond to the Cd concentrations in rice plant. In the field experiment, the Cd concentrations in brown rice of the indica cultivars (i.e., TCS10, TCS17, and TNGS22) were 0.6 mg kg-1; these were significantly higher than those of the japonica cultivars (i.e. TY3, TK9, TNG71, KH145, TKW1, and TKW3). By contrast, the three cultivars, KH145, TKW1, and TKW3, whose Cd concentrations in brown rice were lower than 0.3 mg kg-1 were considered safe relative to the permissible level of 0.4 mg kg-1. In addition, for the used cultivars, Cd concentrations in brown rice were well expressed (i.e., r2 = 0.95) as a function of EC50, M/k, and MDA by using multiple regression. Newly bred cultivars could be screened rapidly with hydroponic testing to predict their Cd concentrations in brown rice when grown in the field.

Effects of Copper on Root Morphology, Cations Accumulation, and Oxidative Stress of Grapevine Seedlings.

In the present study, a hydroponic experiment was conducted to investigate the oxidative stress and the copper (Cu) accumulation in grapevines exposed to three Cu levels (0, 5, and 15 µM) for 1, 2, and 3 days. The results showed that the root elongation was stunted at the highest-exposure concentration. The Cu accumulation in the grapevines increased with increasing Cu treatments, while the other nutrient elements (Ca, Mg and K) absorbed by the grapevines decreased. Most of the Cu taken up by the grapevines was accumulated in the roots. Compared to the data for 1 day after treatment, the Cu-addition significantly decreased the Mg and K concentration in the roots and leaves, yet increased the superoxide dismutase activity in the leaves after 3 days of treatment. For the reactive oxygen species, the malondialdehyde increased with increasing Cu levels in the roots and leaves; however, both the Cu-addition and exposure duration reduced the H2O2 level in the root. Additionally, the Cu-induced accumulation of ·O2- and H2O2 in the grapevine leaves can be observed by the histochemical staining of nitroblue tetrazolium and diaminobenzidine, respectively. In conclusion, the present results indicate that excess Cu results in a change of the root morphology and leads to oxidative stress for the grapevine leaves and roots.

Nonlinear biotic ligand model for assessing alleviation effects of Ca, Mg, and K on Cd toxicity to soybean roots.

Developing a nonlinear biotic ligand model (BLM) that considers the geometrical constraints for binding of different cations on biotic ligands will provide more reliable details about the hypothetical mechanism governing the alleviation of cadmium (Cd) toxicity by coexistent cations. Soybean seedlings under Cd stress produced by various activities of coexistent cations such as calcium (Ca2+), magnesium (Mg2+), and potassium (K+) were hydroponically assayed for Cd toxicity to soybean roots. The Cd2+ activity resulting in 50% reduction of root elongation (RE), EA 50, was used for assessing the Cd toxicity to the soybean seedling. Increasing Ca2+, Mg2+, and K+ activities resulted in a significant alleviation of Cd toxicity to soybean roots. This alleviation was markedly higher with increasing Ca2+ and K+ levels than with increasing Mg2+ level. In addition, EA 50 increased in nonlinear positive relationships with Ca2+ and Mg2+. The real data obtained from the soybean assay were thus used to develop the nonlinear BLM for Cd rhizotoxicity. Two parameters, competition equivalent and stability constant, indicated the profiles of the geometrical constraint and affinity of Ca2+, Mg2+, and K+ binding on the soybean root surface to alleviate Cd toxicity. Compared with the traditional linear BLM, the nonlinear BLM provided more precise predictions of relative root elongation (RRE) and EA 50. Therefore, adopting the nonlinear BLM approach will successfully improve the monitoring and assessment of heavy metal toxicity to terrestrial plants.

Influence of magnesium on copper phytotoxicity to and accumulation and translocation in grapevines.

The phytotoxic effects of excess copper (Cu) on grapevines (Vitis vinifera L. var. Kyoho) were examined, both from macroscopic and microscopic perspectives, by using a fifteen-day hydroponic experiments. The influence of magnesium (Mg) on Cu phytotoxicity to, and accumulation and translocation in grapevines was also observed. For phytotoxicity effect, results showed that a relative low median growth inhibition level of Cu was found for grapevine roots (0.809-3.671µM). Moreover, Cu toxicity was significantly alleviated by Mg treatment at Mg(2+) activity between 0.15 and 2.01mM. For accumulation and translocation effects, results indicated that competition for binding sites between Cu and Mg occurred for roots; however, Mg and Cu levels in stems and leaves were not affected by solution metals concentration. At Cu concentration less than 1µM, the translocation of Cu was decreased significantly for the highest Mg treatment; at Cu concentrations greater than 5µM, no obvious change was observed in leaf TF value between Mg treatments, while an increasing trend of stem TF value was observed with increasing Mg. These results suggest that the toxic effect resulted from metals depend not only on the competition of coexistent cations for plasma membrane surface, but also on the transport and distribution of toxic metals in physiological active sites in plants.

Alleviation effects of magnesium on copper toxicity and accumulation in grapevine roots evaluated with biotic ligand models.

Copper toxicity and accumulation in plants are affected by physicochemical characteristics of soil solutions such as the concentrations of coexistent cations (e.g., Ca(2+), Mg(2+), K(+), Na(+), and H(+)). The biotic ligand model (BLM) approach has been proposed to predict metal phyto-toxicity and -accumulation by taking into account the effects of coexistent cations, given the assumption of the partition equilibrium of metal ions between soil solution and solid phase. The alleviation effects of Mg on Cu toxicity and accumulation in grapevine roots were the main concerns in this study and were investigated by using a hydroponic experiment of grapevine cuttings. The BLM approach, which incorporated competition of Mg(2+) with Cu(2+) to occupy the biotic ligands on root surfaces, was developed to predict Cu rhizotoxicity and accumulation by grapevine roots. In the results, the effective activity of Cu, {Cu (2+)}, resulting in a 50 % reduction of root elongation (EA (50)), linearly increased with increments of Mg activity, {Mg (2+)}. In addition, the Cu concentration in root, Cu ( root ), was retarded by an increase of {Mg (2+)}. The linear model was significantly fitted to the relationship between {Cu (2+)}/Cu ( root ) and {Mg (2+)}. According to the concept of BLM, the present results revealed that the amelioration effects of Mg on Cu toxicity and accumulation in roots could arise from competition between Mg(2+) and Cu(2+) on the binding sites (i.e., the biotic ligands). Then, the developed Cu-BLMs incorporating the Mg(2+) competition effectiveness were validated provide accurate predictions of Cu toxicity and accumulation in grapevine roots. To our knowledge this is the first report of the successful development of BLMs for a woody plant. This BLM approach shows promise of being widely applicable for various terrestrial plants.

Coupling phytotoxicity and human health risk assessment to refine the soil quality standard for As in farmlands.

In the present study, a field experiment was conducted to investigate arsenic (As) concentrations in soils and in grains of 15 rice varieties in a contaminated site in Taiwan. The studied site was divided into two experimental units, namely plot A and plot B. The results showed that mean total As concentrations were 70.94 and 61.80 mg kg-1 in plot A and plot B, respectively, and thus greater than or approximate to the soil quality standard for total As in Taiwan (60 mg kg-1). The As levels in rhizosphere soil in plot A (19.71-32.33 mg kg-1) were much higher than in plot B (6.41-8.60 mg kg-1); however, As accumulation in brown rice did not significantly differ between the plots. These results implied that a significant variation in the bioconcentration factor (BCF) value of As existed among different rice genotypes, and a negative correlation was observed between BCF value and rhizosphere As level in the soil. In phytotoxicity, the median values of the ecological risk indicator were 104.85 and 103.89 in plot A and plot B, respectively, indicating considerable risk. In human health risk assessment, the median and 97.5%-tile values for cancer risk for both male and female residents were markedly higher than the acceptable risk (1 × 10-4). Furthermore, non-cancer and cancer risks were higher for males than females, mainly due to the greater rice ingestion rate of males. Sensitivity analysis showed that total As concentration in soil was the main factor affecting health risks, suggesting that priority should be given to the reduction of soil As levels. To better manage the phytotoxicity of As on rice, as well as the health risk to residents resulting from exposure to As-contaminated soils, the soil quality standard for As in farmland soils should be set between 5 and 10 mg kg-1. The methodology developed in this study could also be applied to provide the basis for refining and revising the soil quality standard for heavy metals in farmland in other regions and countries.

Model evaluation of plant metal content and biomass yield for the phytoextraction of heavy metals by switchgrass.

To better understand the ability of switchgrass (Panicum virgatum L.), a perennial grass often relegated to marginal agricultural areas with minimal inputs, to remove cadmium, chromium, and zinc by phytoextraction from contaminated sites, the relationship between plant metal content and biomass yield is expressed in different models to predict the amount of metals switchgrass can extract. These models are reliable in assessing the use of switchgrass for phytoremediation of heavy-metal-contaminated sites. In the present study, linear and exponential decay models are more suitable for presenting the relationship between plant cadmium and dry weight. The maximum extractions of cadmium using switchgrass, as predicted by the linear and exponential decay models, approached 40 and 34 µg pot(-1), respectively. The log normal model was superior in predicting the relationship between plant chromium and dry weight. The predicted maximum extraction of chromium by switchgrass was about 56 µg pot(-1). In addition, the exponential decay and log normal models were better than the linear model in predicting the relationship between plant zinc and dry weight. The maximum extractions of zinc by switchgrass, as predicted by the exponential decay and log normal models, were about 358 and 254 µg pot(-1), respectively. To meet the maximum removal of Cd, Cr, and Zn, one can adopt the optimal timing of harvest as plant Cd, Cr, and Zn approach 450 and 526 mg kg(-1), 266 mg kg(-1), and 3022 and 5000 mg kg(-1), respectively. Due to the well-known agronomic characteristics of cultivation and the high biomass production of switchgrass, it is practicable to use switchgrass for the phytoextraction of heavy metals in situ.

Toxicokinetics/toxicodynamics with damage feedback improves risk assessment for tilapia and freshwater clam exposed to arsenic.

It has been proposed that irreversible responses of organisms exposed to contaminants are due to a systems-level feedback. Here we tested this hypothesis by reanalyzing the published data on toxicokinetics and survival probability based on a systems-level threshold damage model (TDM) incorporating with a positive damage feedback to explore the steady-state response and dynamic behavior of damage for tilapia and freshwater clam exposed to waterborne arsenic (As). We found that ultrasensitivity appeared in As-tilapia and freshwater clam systems with Hill coefficient n ≥ 4, indicating that the positive damage feedback mechanism has been triggered. We confirmed that damage can trigger a positive feedback loop that together with As stressor increases irreversibility. This study also showed that TDM with positive feedback gave a much better predictability than that of TDM at As concentrations ranging from 100 to 500 mg l(-1) for freshwater clam, whereas for tilapia, two models had nearly same performance on predictability. We suggested that mortality-time profile derived Hill coefficient could be used as a new risk indicator to assess the survival probability for species exposed to waterborne metals. We anticipated that the proposed toxicokinetics/toxicodynamics with a positive damage feedback may facilitate our understanding and manipulation of complex mechanisms of metal susceptibility among species and improve current risk assessment strategies.

The Relationship of Social Media Addiction With Internet Use and Perceived Health: The Moderating Effects of Regular Exercise Intervention.

The popularity of online social media in recent years has not only brought information and social convenience to people's lives, but has also given rise to many problems, among which social media addiction (SMA) has become a concern of many scholars and experts. Past research has shown that regular exercise (REx) can have many health benefits for the body, so numerous scholars and experts believe that this may be one possible strategy for reducing the health effects of online community addiction and Internet use (IU). Therefore, this study adopted a secondary data research approach to explore and predict the effect of age on social media use and personal health, and therefore included age as a control variable to investigate whether the intervention of REx, excluding the effect of age, moderates the effect of SMA on IU and on perceived health (PH). The participants of this study were adults aged 18 years or older in Taiwan, using the 2019 "Survey Research Data Archive," Vol. 7, No. 5 data. A total of 1,933 questionnaires were retrieved, and after elimination of invalid responses, 1,163 data were analyzed using Partial Least Squares Structural Equation Modeling, PLS-SEM. The results were as follows: (1) SMA positively affected IU, (2) SMA could negatively affect PH, (3) there was no statistical effect of IU on PH, (4) SMA did not indirectly affect PH through IU, (5) REx had a moderating effect on SMA and IU, and (6) REx did not regulate the effect of SMA on PH. First, from these results, it is clear that the negative health effects of SMA may not be simply due to prolonged IU. Secondly, while it is true that the moderating effect for people with low levels of SMA can reduce IU, for people with high levels of SMA, the moderating effect of REx becomes a catalyst for increased Internet usage behavior. Finally, we draw conclusions based on the results of the study and propose directions and recommendations for follow-up research.

The influence of motivation, self-efficacy, and fear of failure on the career adaptability of vocational school students: Moderated by meaning in life.

It is an important issue for vocational school students to have good adaptability for their future life. This study combines career construction theory and self-determination theory to construct a model to explore the relationship between the "motivation," "self-efficacy," "fear of failure," "career adaptability," and "meaning in life" of vocational school students. This study used a secondary data research method and retrieved a total of 2,377 data from vocational school students in Taiwan from the perspective of data exploration using PISA 2018 data, which was validated by the partial least squares structural equation model (PLS-SEM). The following results were obtained: (1) Vocational students were afraid that failure would have a negative impact on their career adaptability. (2) Motivation and Self-efficacy had a positive effect on career adaptability. (3) Motivation positively affected fear of failure. (4) Self-efficacy negatively affected fear of failure. (5) Meaning in life could positively moderate the effect of self-efficacy on fear of failure. (6) However, there was no statistical difference in the moderating effect of meaning in life on the relationship between motivation and fear of failure. First, fear of failure negatively affected career adaptability, while motivation and self-efficacy positively affected career adaptability; compared to the three effects, the negative effect of fear of failure may not be as great as expected. Second, motivation is like a double-edged sword as it improves adaptability, but it also comes with an increased fear of failure. On the contrary, self-efficacy can simultaneously improve the career adaptability of vocational students and reduce their fear of failure. Therefore, the development of self-efficacy should be given priority over motivation in the career adaptability enhancement strategy of vocational students. Finally, the meaning of life can positively moderate the negative influence of self-efficacy on the fear of failure. In other words, for vocational students with a low sense of self-efficacy, perhaps life education can be used instead as a strategy to reduce their fear of failure.

Coupling bioaccumulation and phytotoxicity to predict copper removal by switchgrass grown hydroponically.

A major challenge in phytoextraction is to increase plants' removal rates of metals from contaminated soils. In this study, we developed a phytoextraction model, by coupling a saturable Michaelis-Menten type accumulation model and an energy-based toxicity model, to predict copper (Cu) removal by switchgrass (Panicum virgatum L.) grown hydroponically under various exposure concentrations. Results of the present study indicated that the phytotoxicity of Cu to switchgrass is relatively low, whereas a certain accumulation capacity exists in the plant for Cu. In addition, the simulation results suggested that, under a lower dissolved concentration, Cu removal is increased more efficiently as the exposure duration increases. Although it is difficult to extrapolate the results from greenhouse-based hydroponic experiments to field conditions, we believe that the current methodology can offer a first approximation in predicting the phytoextraction duration needed for plant species to remove a specific metal from contaminated sites, which is crucial in evaluating the economic costs for remediation purposes.

Using chemical fractionation to evaluate the phytoextraction of cadmium by switchgrass from Cd-contaminated soils.

The purpose of this study is to evaluate the phytoextraction of cadmium (Cd) from contaminated soils by switchgrass (Panicum virgatum L.), which is a promising energy crop with high biomass. Two ecotypes of switchgrass cultivars, Alamo and Blackwell, were investigated in a pot experiment. Dry weight and plant Cd concentration of the switchgrass plants growing on Cd-spiked soils (0, 20, and 60 mg Cd kg(-1) soil) with chelating agent amendments (1 g kg(-1) citric acid [CA] and 0.1 g kg(-1) ethylene diaminetetraacetic acid [EDTA]) were measured to examine the phytotoxicity and accumulation of Cd in the switchgrass. Fractions of Cd (F1, exchangeable; F2, carbonate; F3, Fe-Mn oxide; F4, organic matter; F5, residual) for the soils sampled at the time of harvesting were also determined using chemically sequential extractions. In the results, the dry weight of the switchgrass decreased with increasing Cd, with a significant dry weight reduction when Cd exceeded 20 mg kg(-1). However, the high Cd spike of 60 mg kg(-1) was not lethal to Alamo and Blackwell, which suggests that switchgrass plants can tolerate Cd and grow in contaminated soils. Compared with the control, the CA and EDTA amendments had no adverse effect on the growth of switchgrass plants. With regard to Cd accumulation, higher plant Cd concentrations were frequently found after CA amendment in Alamo; however, the Cd concentrations of Blackwell plants may increase when amended with EDTA. On the basis of the fractionation of soil Cd, dry weight and plant Cd concentration could be expressed as a function of Cd fractionation to predict the phytoextraction of Cd. Thus, the fractionation of Cd is a useful approach for evaluating the phytoextraction of Cd by switchgrass in contaminated soils. According to the comparison of phytoextractions of Cd between Alamo and Blackwell, Alamo plants removed substantially more Cd from Cd-spiked soils than Blackwell. Therefore, Alamo is better suited for the phytoextraction of Cd from contaminated soils.

Assessing abalone growth inhibition risk to cadmium and silver by linking toxicokinetics/toxicodynamics and subcellular partitioning.

The purpose of this study was to link toxicokinetics/toxicodynamics and subcellular partitioning for assessing the susceptibility and the growth inhibition risks of abalone Haliotis diversicolor supertexta exposed to waterborne and foodborne cadmium (Cd) and silver (Ag). We reanalyzed published data on growth inhibition and subcellular partitioning associated with the present mechanistic model to explore the correlations among elimination (k (e)), detoxification (k (d)), and recovery (k (r)) rate constants and to assess the growth inhibition risk. We found a positive correlation among k (e), k (d), and k (r) in abalone exposed to Ag. We also employed a life-stage based probabilistic assessment model to estimate the growth inhibition risk of abalone to environmentally relevant Cd (5-995 µg l(-1)) and Ag (0.05-9.95 µg l(-1)) concentrations in Taiwan. The results showed that abalone had a minimum 20% probability of the growth inhibition risk exposed to Cd, whereas Ag exposure was not likely to pose the risk. The maximum biomasses were estimated to be 0.0039 and 0.0038, 61.61 and 43.87, and 98.88 and 62.97 g for larvae, juveniles, and adults of abalone exposed to the same levels of Cd and Ag, respectively. Our study provides a useful tool to detect potential growth biomass of abalone populations subjected to Cd and Ag stresses and mechanistic implications for a long-term ecotoxicological risk assessment in realistic situations.

Assessing human health risk of arsenic for rice consumption by an iron plaque based partition ratio model.

A field experiment was conducted to study the transport and uptake of arsenic (As) from soil to rice roots and the subsequent translocation from roots to shoots and grains. Twelve rice cultivars were used in the field experiment. The amount of As accumulated in rice grains and sequestered by root iron plaque and rhizosphere soil, were determined to establish the relationship between As concentrations in brown rice and As sequestration by iron oxides. Human health risk was then assessed for Taiwan's population exposed to As through rice consumption. The result of this study showed that the mean total As concentrations in the experimental site and in brown rice were 93.02 mg/kg and 0.158 mg/kg, respectively. The As sequestration by iron oxides on root plaque (3.48-9.51) was higher than that of the rhizosphere soil (1.86-4.09) for all tested rice cultivars. Therefore, the partition ratio (PR) representing the relative tendency of As sequestration by rhizosphere soil to that in root iron plaque was all less than 1. In addition, there was a significant negative linear relationship between inorganic As concentration (iAs) in brown rice and PR value (r2 = 0.38, p < 0.05). Based on the iAs in brown rice, the median value of hazard quotient (HQ) and target cancer risk (TR) was 1.13 and 5.10 × 10-4, respectively, indicating potential cancer and non-cancer risk for Taiwan residents exposed to As through the consumption of rice grown on the studied site. Various PR values were then successfully used for estimating risk, implying that screening the PR of the rice plant before harvest could serve as an early warning signal for protecting consumers' health. However, more experiments with different rice cultivars for the paddy soils were suggested in the future to establish a comprehensive relationship between iAs in brown rice and PR value.

Aspects of cultivar variation in physiological traits related to Cd distribution in rice plants with a short-term stress.

BACKGROUND: Genotypic variations are seen in cadmium (Cd) tolerance and accumulation in rice plants. Cultivars that show low Cd translocation from the root into shoot can be selected to reduce Cd contamination in rice grains. This study aims to clarify the physiological regulation related to Cd absorption by rice plants for screening out the cultivars, which have relatively low Cd accumulation in grains. Eight Taiwan mega cultivars of paddy rice: japonica (TY3, TK9, TNG71, and KH145 cultivars), indica (TCS10 and TCS17 cultivars), and glutinous (TKW1 and TKW3 cultivars), which are qualified with the criteria for rice grain quality by the Council of Agriculture, Taiwan, were used for illustration. An experiment in hydroponics was conducted for the rice seedlings with a treatment of 50 µM CdCl2 for 7 days. RESULTS AND DISCUSSION: After the Cd treatment, the reductions in shoot growth were more significant than those in root growth; however, Cd absorbed in the rice plant was sequestered much more in the root. The malondialdehyde (MDA) was preferentially accumulated in rice root but the hydrogen peroxide (H2O2) was increased more significantly in the shoot; the antioxidative enzymes, superoxide dismutase (SOD) and ascorbate peroxidase (APX), were pronounced more in rice shoot. CONCLUSIONS: The rice cultivars preferentially accumulated Cd in the root rather than the shoot with the Cd treatment, which resulted in significant enhancements of MDA and growth reductions in the root. However, H2O2 accumulation was toward the shoot to retard shoot growth suddenly and then the root could keep a gradual growth. Also, the rice cultivars, which preferentially accumulate Cd in the root, would have the regulation tendency of SOD toward the shoot. Due to that SOD is responsible for H2O2 production, H2O2 accumulation would be thus toward the shoot. Moreover, the cultivars, which have a less regulation tendency of APX toward the shoot, would present higher translocation of Cd into the shoot.

A biotic ligand model-based toxicodynamic approach to predict arsenic toxicity to tilapia gills in cultural ponds.

Farming of tilapia Oreochromis mossambicus is an important aquacultural activity in Taiwan. Due to the elevated arsenic (As) concentration in pond water, it is important to assess the bioavailability and toxicity of As to tilapia for protection of aquatic life and human health. In the present study, we developed a biotic ligand model (BLM)-based toxicodynamic approach to dynamically predict both acute and chronic effective concentrations of As to tilapia in two tilapia farms located at Pudai and Chiangchun counties in southwestern Taiwan. Parameters revealed in the mechanistic model were obtained by fitting this model to the toxicokinetic and toxicodynamic data from our previous laboratory experiments. Based on our extended BLM concepts, the site-specific water effect ratios and ambient water quality criteria can be determined with known water chemistry. The proposed methodology was capable of bridging the gap between laboratory toxicity bioassays and field investigations. With respect to risk assessments, our research may also provide an useful means of generating and adjusting the site-specific ambient water quality criteria.

Sensory determinants of valve rhythm dynamics provide in situ biodetection of copper in aquatic environments.

This study successfully applied an improved valvometry technique to measure waterborne copper (Cu), based on valve activity dynamics of the freshwater clam Corbicula fluminea. The improved valvometry technique allows the use of free-range bivalves and avoids causing stresses from experimental artifacts. The proposed daily valve rhythm models and a toxicodynamics-based Hill model were linked to predict valve dynamic responses under different Cu exposures with a circadian valve rhythm endpoint. Cu-specific detection threshold was 5.6 (95 % CI 2.1-9.3) and 19.5 (14.6-24.3) µg L(-1) for C. fluminea, based on response times of 300 and 30 min, respectively. Upon exposure to Cu concentrations in excess of 50 µg L(-1), the alteration of valve rhythm behavior was correlated with Cu concentration within 30 min, indicating notable sensing ability. This study outlines the feasibility of an in situ early warning dynamic biomonitoring system for detection of waterborne Cu based on circadian valve activities of C. fluminea.

Risk-based approach to appraise valve closure in the clam Corbicula fluminea in response to waterborne metals.

We developed a risk-based approach to assess how the valve closure behavior of Asiatic clam Corbicula fluminea responds to waterborne copper (Cu) and cadmium (Cd). We reanalyzed the valve closure response data from published literature to reconstruct the response time-dependent dose-response profiles based on an empirical three-parameter Hill equation model. We integrated probabilistic exposure profiles of measured environmental Cu and Cd concentrations in the western coastal areas of Taiwan with the reconstructed dose-response relationships at different integration times of response to quantitatively estimate the valve response risk. The risk assessment results implicate exposure to waterborne Cu and Cd may pose no significant risk to clam valve activity in the short-time response periods (e.g., <30 min), yet a relative high risk for valve closure response to waterborne Cu at response times greater than 120 min is alarming. We successfully linked reconstructed dose-response profiles and EC50-time relationships associated with the fitted daily valve opening/closing rhythm characterized by a three-parameter lognormal function to predict the time-varying bivalve closure rhythm response to waterborne metals. We parameterized the proposed predictive model that should encourage a risk-management framework for discussion of future design of biological monitoring systems.