Hung-Yu Lai

Remediation techniques and heavy metal uptake by different rice varieties in metal-contaminated soils of Taiwan: New aspects for food safety regulation and sustainable agriculture

Abstract Rice is one of the most important staple foods worldwide. Soil contamination with heavy metals and food safety problems occur in many countries as a result of numerous human activities, particularly wastewater and solid waste disposal. This review paper provides a schematic summary of heavy metals in identification processes, transport in soil to different rice varieties, and soil remediation strategies and techniques surrounding the agro-environmental impact in paddy soils based on a description of Taiwan’s experiences and database. In terms of the soil control standard, heavy metals including As, Cd, Cr, Cu, Hg, Ni, Pb and Zn are regulated by the Soil and Ground ater Pollution Remediation Act of Taiwan. Owing to the heavy metal source from wastewater along irrigation systems, heavy metals not only accumulate in the surface soil (0–30 cm), but are also highly distributed at the main entrance of irrigation water into individual paddy fields. Moreover, sediments in the irrigation canal have to be dredged and the irrigation system needs to be isolated from the discharge system of wastewater to maintain soil quality. Cadmium in rice grains accumulates more significantly in Indica varieties than in Japonica varieties, and this accumulation exceeds the food quality standard. The best well-performing metal uptake models have been developed to predict Cd levels in rice grains for Indica and Japonica varieties using soil bioavailable Cd and Zn concentrations extracted by 0.01 mol L−1 CaCl2. Soil remediation techniques, including turnover and dilution, in situ stabilization by chemical amendments and phytoremediation, have been tested and recommended in Taiwan. Although the high background levels of As, Cr and Ni, which were higher the soil control standard in some paddy soils, are derived from andesite and serpentinites in Taiwan, rice quality and yield were not adversely affected by these metals when labile concentrations were very low. Overall, it is necessary to identify the bioavailability of heavy metals in different soil types from specific case studies to provide reliable parameters for health-based risk assessments and to further achieve the goal of food safety and sustainable agriculture.

Health risk-based assessment and management of heavy metals-contaminated soil sites in Taiwan.

Risk-based assessment is a way to evaluate the potential hazards of contaminated sites and is based on considering linkages between pollution sources, pathways, and receptors. These linkages can be broken by source reduction, pathway management, and modifying exposure of the receptors. In Taiwan, the Soil and Groundwater Pollution Remediation Act (SGWPR Act) uses one target regulation to evaluate the contamination status of soil and groundwater pollution. More than 600 sites contaminated with heavy metals (HMs) have been remediated and the costs of this process are always high. Besides using soil remediation techniques to remove contaminants from these sites, the selection of possible remediation methods to obtain rapid risk reduction is permissible and of increasing interest. This paper discusses previous soil remediation techniques applied to different sites in Taiwan and also clarified the differences of risk assessment before and after soil remediation obtained by applying different risk assessment models. This paper also includes many case studies on: (1) food safety risk assessment for brown rice growing in a HMs-contaminated site; (2) a tiered approach to health risk assessment for a contaminated site; (3) risk assessment for phytoremediation techniques applied in HMs-contaminated sites; and (4) soil remediation cost analysis for contaminated sites in Taiwan.

Effects of Nitrogen Fertilizers on the Growth and Nitrate Content of Lettuce (Lactuca sativa L.)

Nitrogen is an essential element for plant growth and development; however, due to environmental pollution, high nitrate concentrations accumulate in the edible parts of these leafy vegetables, particularly if excessive nitrogen fertilizer has been applied. Consuming these crops can harm human health; thus, developing a suitable strategy for the agricultural application of nitrogen fertilizer is important. Organic, inorganic, and liquid fertilizers were utilized in this study to investigate their effect on nitrate concentrations and lettuce growth. The results of this pot experiment show that the total nitrogen concentration in soil and the nitrate concentration in lettuce increased as the amount of nitrogen fertilizer increased. If the recommended amount of inorganic fertilizer (200 kg·N·ha−1) is used as a standard of comparison, lettuce augmented with organic fertilizers (200 kg·N·ha−1) have significantly longer and wider leaves, higher shoot, and lower concentrations of nitrate.

Subcellular distribution and chemical forms of cadmium in Impatiens walleriana in relation to its phytoextraction potential.

Impatiens (Impatiens walleriana) has been shown to be a potential cadmium (Cd) hyperaccumulator, but its mechanisms in accumulation and detoxification have not been reported. Rooted cuttings of Impatiens were planted in artificially Cd-contaminated soils for 50 days with total target concentrations of 0, 10, 20, 40, 80, and 120 mg/kg. The subcellular distribution and chemical forms of Cd in the different organs were analyzed after the pot experiment. Compared with the control group, various Cd treatments affected the growth exhibitions of Impatiens, but most of them were not statistically significant. The Cd accumulation of different organs increased with an increase in the soil Cd concentrations for most of the treatments, and it was in the decreasing order of root>stem>leaf. In the roots of Impatiens, Cd was mainly compartmentalized in the soluble fraction (Fs), which has a high migration capacity and will further translocate to the shoot. The Cd was mainly compartmentalized in the cell wall fraction (Fcw) in the shoots as a mechanism of tolerance. Most of the Cd in the various organs of Impatiens was mainly in the forms of pectate and protein-integrated (FNaCl), whereas a minor portion was a water soluble fraction (FW). The experimental results show that the Cd in the Fs, FW, and FNaCl in the roots of Impatiens had a high mobility and will further translocate to the shoot. They could be used to estimate the Cd accumulated in the shoots of Impatiens.

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.

Large-Area Experiment on Uptake of Metals by Twelve Plants Growing in Soils Contaminated with Multiple Metals

A site in central Taiwan with an area of 1.3 ha and contaminated with Cr, Cu, Ni, and Zn was selected to examine the feasibility of phytoextraction. Based on the results of a pre-experiment at this site, a total of approximately 20,000 plants of 12 species were selected from plants of 33 tested species to be used in a large-area phytoextraction experiment at this site. A comparison with the initial metal concentration of 12 plant species before planting demonstrated that most species accumulated significant amounts of Cr, Cu, Ni, and Zn in their shoots after growing in this contaminated site for 31 d. Among the 12 plant species, the following accumulated higher concentrations of metals in their shoots; Garden canna and Garden verbena (45–60 mg Cr kg−1), Chinese ixora and Kalanchoe (30 mg Cu kg−1), Rainbow pink and Sunflower (30 mg Ni kg−1), French marigold and Sunflower (300–470 mg Zn kg−1). The roots of the plants of most of the 12 plant species can accumulate higher concentrations of metals than the shoots and extending the growth period promotes accumulation in the shoots. Large-area experiments demonstrated that phytoextraction is a feasible method to enable metal-contaminated soil in central Taiwan to be reused.

Chelator effects on bioconcentration and translocation of cadmium by hyperaccumulators, Tagetes patula and Impatiens walleriana.

French marigold (Tagetes patula) and impatiens (Impatiens walleriana) can act as hyperaccumulator plants for removal of cadmium (Cd) from contaminated sites. In this study, an exponential decay model was used to predict the maximum removal of Cd from artificially spiked soils by impatiens. Application of a chelator, EDTA, was also assessed for effects on the bioconcentration (BCF) and translocation (TF) factors of the two species with four replicates. Exposure to Cd significantly decreased the biomass of two plant species. Impatiens and French marigold accumulated Cd at a rate of 200-1200 mg Cd kg(-1) in shoots, with BCFs and TFs of 8.5-15 and 1.7-2.6, respectively.

Copper concentrations in grapevines and vineyard soils in central Taiwan

Abstract The main purpose of the present study was to conduct a field investigation to map copper (Cu) vertical distribution in vineyard soils and to investigate the Cu contents in shoots, leaves, and grapes of grapevines in the studied plots in central Taiwan. The mean total Cu concentrations in vineyard soils of the present study ranged from 9.1 to 100 mg kg−1, which were lower than those reported in other vine-growing areas in Brazil and parts of Europe, yet well within the range of those in Canada, Australia, and New Zealand. The Cu concentration in grapevine organs was found to be highest in the leaves, followed by the perennial wood parts, annual shoots, and grapes. The bioaccumulation factors in various organs of the grapevines were mostly greater than unity, indicating that a process of bioaccumulation of Cu occurred in the soil-grapevine system. Results of the present study can be used as one of the risk management factors in making the final decision in examining and refining the existing trigger level of Cu at vine-growing areas.

POT EXPERIMENT TO STUDY THE UPTAKE OF CD AND PB BY THREE INDIAN MUSTARDS (BRASSICA JUNCEA) GROWN IN ARTIFICIALLY CONTAMINATED SOILS

Most of the metals-contaminated and fallow lands in Taiwan are a result of irrigation with illegal effluent of factories. Phytoextraction methods can be applied to reach the target of fallow-lands reuse and earn more incomes for farmers. In many studies, Indian mustards (Brassica juncea) were planted in the metal-contaminated soils to study their suitability in phytoextraction. However, the total removal of metals by plants was quite different between accessions. In this pot study, three accessions of B. juncea (cv. 182921, cv. 211000, and cv. 426308) were planted in artificially Cd- or Pb-contaminated soils to investigate the differences between them. EDTA was applied to study its effect in increasing the bioavailability of Cd and Pb and their uptake by these Indian mustards. Experimental result showed that three accessions of Indian mustard can accumulate a high concentration of Cd and Pb when growing in the artificially Cd- and Pb-contaminated soils. Their shoot Cd or Pb concentrations were significantly enhanced, resulting from the application of EDTA. Among the three accessions, B. juncea cv. 211000 accumulated the highest concentrations of Cd and Pb in their shoots compared with B. juncea cv. 182921 and cv. 426308, but its total removal was the lowest due to its lower biomass.

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.