Influence of soil amendments on phytostabilization, localization and distribution of zinc and cadmium by marigold varieties

Marigolds (Tagetes erecta L.) were evaluated for phytoremediation potential of cadmium (Cd) and zinc (Zn) as a function of amendment application to soil. Vermicompost (V), biodigestate (Bi), and combined V + Bi (VBi) were used as soil amendments in Zn and Cd co-contaminated soils. Application of soil amendments can alter physicochemical properties of soils, particularly pH, EC, CEC and nutrient concentrations. The VBi treatment resulted in highest percentage growth rate in biomass (52 %) for the Twenty yellow variety of marigold. Also, in the VBi treatment, leaves of Dragon yellow variety exhibited maximal accumulation of Zn and Cd. Flower extracts of Twenty yellow in the V treatment had substantial carotenoid content (71.7 mg L-1) and lowest IC50 value (43.7 mg L-1), thus indicating it had highest DPPH free radical scavenging activity. Dragon yellow exhibited highest values of ferric reducing antioxidant power (FRAP; 2066 mg L-1), total flavonoids content (TFC; 64.1 mg L-1), and total phenolics content (TPC; 50.9 mg L-1). Using X-ray fluorescence (XRF) spectroscopy, the atomic percentages of Zn and Cd in all marigold varieties and treatments showed similar patterns over flower surfaces, seeds, and flower petals in descending order. Prime yellow in the V treatment resulted in higher Zn accumulation in roots (bioconcentration factor of root value) > 1 and translocation factor value < 1, indicating an enhanced ability of the plant for phytostabilization. Application of V altered antioxidant activities and production of bioactive compounds as well as enhanced the excluder potential of Cd and Zn, particularly in the Prime yellow variety. Application of Bi contributed to increased flower numbers, suggesting that floriculturists cultivating marigolds for ornamental purposes may be able to generate revenue in terms of productivity and quality of flowers when marigolds are grown on contaminated land.

Necrophagous flies as bioindicators in Cd and Zn co-contaminated areas of Tak Province, Thailand

Necrophagous flies may be effective bioindicators of chemical substances within polluted locations, as they are sensitive to environmental changes, have large populations, and thrive in a single location over their lifespan. Diversity and abundance of necrophagous flies were determined at livestock farms contaminated with potentially toxic elements (PTEs) in Tak Province and Nakhon Sawan Province, Thailand. Substantial soil zinc (Zn) concentrations (> 1100 mg kg-1) were detected at a cattle farm at Khaothong, Nakhon Sawan Province, and soil cadmium (Cd) values were significantly elevated (> 3 mg kg-1) at a cattle farm in Pha De, Tak Province. Anthropogenic inputs including Zn mining, domestic wastewater, and certain materials used in local agriculture were point sources of PTEs at the livestock farms in the Pha De and Khaothong subdistricts. Lower temperatures and humidity during the rainy season may have resulted in increased numbers of necrophagous flies, which was 1.5 times greater compared to the dry season. However, the dry season exhibited a higher PTE buildup in fly tissue. The order of important value index (IVI) values of the necrophagous flies were: Chrysomya megacephala (56.80), Musca domestica (27.21), C. rufifacies (25.40) and Sarcophaga spp. (17.54), respectively. These necrophagous flies may play a significant role in PTE-contaminated ecosystems based on their high IVI values, suggesting that they could be used as bioindicators of PTEs. Principal component analysis (PCA) results for necrophagous flies associated with each sampling site during the dry season were consistent with flies having substantial IVI values. Musca domestica and C. megacephala of both sexes displayed substantial correlations with Cr, Al, and Mn, while females of Sarcophaga spp. displayed strong associations with Cd. At the cattle farm in Khaothong, males of M. domestica showed a significant relationship with Zn, Cu, Pb, and Ni. When considering PTE accumulation capacity in flies commonly found at field sites, C. megacephala and M. domestica are the most suitable bioindicators of PTEs. This study confirms that necrophagous flies serve as reliable bioindicators of PTE pollution.

Alleviation of Cadmium Toxicity in Thai Rice Cultivar (PSL2) Using Biofertilizer Containing Indigenous Cadmium-Resistant Microbial Consortia

Biofertilizer as an amendment has growing awareness. Little attention has been paid to bioremediation potential of indigenous heavy-metal-resistant microbes, especially when isolated from long-term polluted soil, as a bioinoculant in biofertilizers. Biofertilizers are a type of versatile nutrient provider and soil conditioner that is cost-competitive and highly efficient with nondisruptive detoxifying capability. Herein, we investigated the effect of biofertilizers containing indigenous cadmium (Cd)-resistant microbial consortia on rice growth and physiological response. The Thai rice cultivar PSL2 (Oryza sativa L.) was grown in Cd-enriched soils amended with 3% biofertilizer. The composition of the biofertilizers' bacterial community at different taxonomic levels was explored using 16S rRNA gene Illumina MiSeq sequencing. Upon Cd stress, the test biofertilizer had maximum mitigating effects as shown by modulating photosynthetic pigment, MDA and proline content and enzymatic antioxidants, thereby allowing increased shoot and root biomass (46% and 53%, respectively) and reduced grain Cd content, as compared to the control. These phenomena might be attributed to increased soil pH and organic matter, as well as enriched beneficial detoxifiers, i.e., Bacteroidetes, Firmicutes and Proteobacteria, in the biofertilizers. The test biofertilizer was effective in alleviating Cd stress by improving soil biophysicochemical traits to limit Cd bioavailability, along with adjusting physiological traits such as antioxidative defense. This study first demonstrated that incorporating biofertilizer derived from indigenous Cd-resistant microbes could restrict Cd contents and consequently enhance plant growth and tolerance in polluted soil.

Effects of copper accumulation on growth and development of Scopelophila cataractae grown in vitro

Scopelophila cataractae was cultured in vitro for 16 weeks to assess the contrasting effects of Cu on growth and reproduction, as well as gametophore stage. To induce buds and gametophores of S. cataractae, ten treatments (tr 1 to tr 10) of culture media were prepared using a combination of mineral salts, sugar, vitamin B complex, CuSO₄, and exogenous hormones. Highest numbers of gametophores and buds were formed in media containing 500 µM CuSO₄ in co-application with auxin and cytokinin, as shown in the modest Cu treatments (tr 6 and tr 7, 26 per cushion and 255 per 25 mm², respectively). A 5000 µM CuSO₄ concentration inhibited development of protonema, possibly due to Cu toxicity, resulting in chloronema forming contorted filaments or short cells containing lipid bodies, and brood body diaspores but no gametophore or bud formation. In this study, S. cataractae Cu accumulation in tissue was substantial (up to 2843.1 mg kg^-1; tr 6) with no or minimal adverse effects, reflecting its potential for phytoremediation of Cu in terrestrial and aquatic ecosystems. The highest atomic percentages of Cu and Zn were detected in the stem surfaces of gametophores treated with 500 µM CuSO₄ (11% atomic Cu and 7% atomic Zn), which served as a primary heavy metal storage site, ultimately protecting cells from metal toxicity. The success of this in vitro study on S. cataractae should also aid ex situ conservation efforts for a variety of rare moss taxa in the wild.

The bryophyte community as bioindicator of heavy metals in a waterfall outflow

The species diversity and heavy metal accumulation in bryophytes were determined in Huay Pah Lahd stream in Doi Suthep-Pui National Park, Thailand. Eight bryophytes from two major taxonomic groupings (epilithic mosses and liverworts) were investigated. Of these, Fissidens crispulus var. crispulus was the most dominant taxon with an importance value (IV) of 28.98%, while Ectropothecium zollingeri, Claopodium prionophyllum, and Hyophila involuta were also dominant taxa with IV ≥ 10%. Scopelophila cataractae, a rare moss species with the lowest IV (0.91%) had the greatest capacity to accumulate metals in tissue, particularly Fe, Zn, Cd and Cu in protonemata (8026.7, 1187.2, 16.9 and 530.1 mg kg⁻¹, respectively). The highest enrichment factors (EFs) of Zn, Cd and Cu (5.3, 2.4 and 0.9, respectively) were also found in S. cataractae, while the highest EF_Mn (1.1) was found in H. involuta. Enrichment factors of most heavy metals were < 5 from the study bryophytes, which suggests that natural processes were the key source of heavy metals. Dilution effects caused by increased water volume during the rainy season may be responsible for low pollutant loads and the maintenance of good water quality in this waterfall stream, which is favorable for biota and general environmental health.

Effects of Soil Amendments on Metal Uptake, Antioxidant Activities and Production of Bioactive Compounds by Sunflower Sprouts

The effects of soil amendments on Cd and Zn uptake, bioactive compounds and antioxidant activities in two cultivars (Pacific 33 and Black Oil) of Helianthus annuus L. were evaluated. Dicalcium phosphate/cattle manure and leonardite/cattle manure mixed in a 1:1 w/w ratio with soil served as soil treatments. The Black Oil cultivar experienced greater metal uptake, biomass production and survival rate compared to the Pacific 33 cultivar. The increased Cd and Zn uptake (>0.2 and >99.4 mg/kg, respectively) in Black Oil cultivar exceeded the regulatory standard for vegetables. Significantly higher levels of bioactive compounds and antioxidant activities were detected in the control treatment for Pacific 33 leaves compared to Black Oil cultivar. Synergistic effects of heavy metals, amendment application and plant genotype are considered key factors in decreased levels of bioactive compounds and antioxidant activities.

Heavy Metal Accumulation and Copper Localization in Scopelophila cataractae in Thailand

Four specimens of gametophores and protonemata of Scopelophila cataractae (copper moss) were collected from a stream in Doi Suthep-Pui National Park, Thailand in order to determine heavy metal accumulation and Cu localization. The order of total metal concentrations in the protonemata and leaf cell surfaces of S. cataractae was Fe > Zn > Cu. Significant Cu values (> 400 mg kg^-1) were found in both gametophores and protonemata. Growth substrates were considered as a key source of heavy metals in the sampling stream. X-ray spectrometry (EDS micro-analyser) detected the localization of ten elements (C, O, Mg, Al, Si, Ca, S, Cu, Zn and In); substantial atomic percentages of Al, Cu and Zn were noted in leaf surfaces and protonemata. These metallic elements were found in highest proportion. To some extent, cell surfaces at the basal leaf costa showed the highest peak value compared to medial and apical leaf portions (≈ 4.3 at.%). This Cu moss can be used as a bioindicator to reflect anthropogenic activities in stream ecosystems.

Cadmium (Cd) and zinc (Zn) accumulation by Thai rice varieties and health risk assessment in a Cd-Zn co-contaminated paddy field: Effect of soil amendments

Zinc mining and smelting activities result in cadmium (Cd) and zinc (Zn) contamination in rice grains, causing deleterious impacts on human health and local economies. Here, we investigated the effects of soil amendments, including mixtures of dicalcium phosphate with cattle manure (T1) and leonardite (T2), on soil physicochemical properties as well as growth performance and accumulation of Cd and Zn among three commercial Thai rice varieties: Khao Dok Mali 105 (KDML105), Phitsanulok2 (PSL2) and RD3, grown in a Cd-Zn co-contaminated paddy field. Human health risk was assessed using the health risk index (HRI) and Daily Intake of Metal (DIM). Application of the amendments, particularly T1, decreased Cd and Zn bioavailability by 60% and 39%, respectively, increased biomass production in PSL2 and RD3 varieties, and substantially reduced Cd uptake in the KDML105 variety by 47%. While levels of Zn in whole plant tissues of all treatments did not exceed maximum levels of undesirable substances in fodder, Cd contents in grain of PSL2 and RD3 exceeded the maximum allowable concentration of 0.2 mg kg^-1. The HRI values for Cd of PSL2 and RD3 varieties were relatively high and are considered to pose a potential risk to human health. KDML105 in the T1 treatment had the lowest HRI value (0.05 ± 0.03), which was within acceptable limits. Our results suggest that Cd and Zn accumulation in rice and associated human health risks could be reduced by application of amendments to paddy soils, but the effectiveness depends on amendment types, rice varieties and soil physicochemical properties.

Effects of soil amendments on leaf anatomical characteristics of marigolds cultivated in cadmium-spiked soils

The marigolds (Tagetes spp.) in this study were classified as excluders for cadmium (Cd); however, their leaves also accumulated substantial Cd content. Among the experimental treatments (i.e., control, cattle manure, pig manure, and leonardite which served as soil amendments), pig manure resulted in significantly increased growth performance for all marigold cultivars as seen by relative growth rates (119-132.3%) and showed positive effects on leaf anatomy modifications, e.g., thickness of spongy and palisade mesophyll, size of vein area and diameter of xylem cells. This may be due to substantially higher essential nutrient content, e.g., total nitrogen (N) and extractable phosphorus (P), in pig manure that aided all marigold cultivars, particularly the French cultivar which exhibited the highest relative growth rate (132.3%). In the Cd-only treatment, cell disorganization was observed in vascular bundles as well as in palisade and spongy mesophyll, which may have been responsible for the lowest plant growth performance recorded in this study, particularly among the American and Honey cultivars (RGR = 73% and 77.3%, respectively).

Potential of ornamental monocot plants for rhizofiltration of cadmium and zinc in hydroponic systems

Cadmium (Cd) and zinc (Zn) accumulation and uptake ability have been investigated in three ornamental monocot plants (Heliconia psittacorum x H. spathocircinata, Echinodorus cordifolius, and Pontederia cordata) grown in hydroponic systems. All study plants in the highest heavy metal treatments were found to be excluders for Cd and Zn with translocation factor values < 1 and bioconcentration factor (BCF) values > 100. The highest Cd and Zn accumulations were found in roots of E. cordifolius (4766.6 mg Zn kg^-1 and 6141.6 mg Cd kg^-1), followed by H. psittacorum x H. spathocircinata (4313.5 mg Zn kg^-1) and P. cordata (3673.3 mg Cd kg^-1), respectively, whereas shoots had lower performances. However, P. cordata had the lowest dry biomass production compared to the other two plant species in this study. As a result of dilution effects, heavy metal accumulation for all study plants was lower in the combined heavy metal treatments than in solely Cd and Zn only treatments. At the end of experiments, the highest uptakes of Cd and Zn were found in H. psittacorum x H. spathocircinata (62.1% Zn²⁺ from 10 mg Zn L^-1 solution) and E. cordifolius (27.3% Cd²⁺ from 2 mg Cd L^-1 solution). Low percentage metal uptakes were found in P. cordata; therefore, E. cordifolius and H. psittacorum x H. spathocircinata are clearly better suited for removing Cd and/or Zn from contaminated waters and hydroponic systems.

Potential of ornamental monocot plants for rhizofiltration of cadmium and zinc in hydroponic systems

Cadmium (Cd) and zinc (Zn) accumulation and uptake ability have been investigated in three ornamental monocot plants (Heliconia psittacorum x H. spathocircinata, Echinodorus cordifolius, and Pontederia cordata) grown in hydroponic systems. All study plants in the highest heavy metal treatments were found to be excluders for Cd and Zn with translocation factor values < 1 and bioconcentration factor (BCF) values > 100. The highest Cd and Zn accumulations were found in roots of E. cordifolius (4766.6 mg Zn kg^-1 and 6141.6 mg Cd kg^-1), followed by H. psittacorum x H. spathocircinata (4313.5 mg Zn kg^-1) and P. cordata (3673.3 mg Cd kg^-1), respectively, whereas shoots had lower performances. However, P. cordata had the lowest dry biomass production compared to the other two plant species in this study. As a result of dilution effects, heavy metal accumulation for all study plants was lower in the combined heavy metal treatments than in solely Cd and Zn only treatments. At the end of experiments, the highest uptakes of Cd and Zn were found in H. psittacorum x H. spathocircinata (62.1% Zn²⁺ from 10 mg Zn L^-1 solution) and E. cordifolius (27.3% Cd²⁺ from 2 mg Cd L^-1 solution). Low percentage metal uptakes were found in P. cordata; therefore, E. cordifolius and H. psittacorum x H. spathocircinata are clearly better suited for removing Cd and/or Zn from contaminated waters and hydroponic systems.

Phytoremediation of engineered nanoparticles using aquatic plants: Mechanisms and practical feasibility

Certain plants have demonstrated the capability to take up and accumulate metals, thus offering the potential to remediate metal-contaminated water and sediment. Several aquatic species have further been identified which can take up metal and metal oxide engineered nanoparticles (ENPs). It is important to evaluate if aquatic plants exhibiting potential for metal phytoremediation can be applied to remediation of metallic ENPs. Understanding the interactions between ENPs and aquatic plants, and evaluating possible influences on metal uptake and phytoremediation processes is therefore essential. This review article will address the feasibility of green plants for treatment of ENP-affected aquatic ecosystems. Discussion will include common types of ENPs in current use; transformations of ENPs in aquatic systems; the importance of microorganisms in supporting plant growth; ENP entry into the plant; the influence of microorganisms in promoting plant uptake; and recent findings in phytoremediation of ENP-affected water, including applications to constructed wetlands.

Soil amendments for cadmium phytostabilization by five marigold cultivars

In recent years, ornamental plants have come under investigation as phytoremediation agents. In addition to reducing contaminant concentrations in soil, such plants support local economies by serving social (e.g., religious) and decorative purposes. Greenhouse studies investigated the phytostabilization potential of soil cadmium (Cd) by five cultivars of marigold (Tagetes erecta), a common ornamental flower in Asia. The effects of organic (cattle manure and pig manure) and inorganic (leonardite and Osmocote®) amendments in supporting plant growth and enhancing Cd uptake were also examined. Marigold cultivars Babuda and Sunshine grown in soil supplemented with pig manure produced the greatest biomass and experienced greatest Cd accumulation and flower production. In all treatments, plant parts accumulated Cd in the following order: root > shoot ≈ flower. Furthermore, Babuda and Sunshine cultivars had a high phytostabilization potential as evidenced by translocation factors < 1 and bioconcentration factors > 1 for roots. It is proposed that Babuda and Sunshine marigold cultivars be applied toward Cd phytostabilization while enhancing local economies as an ornamental species.

Root system architecture influencing cadmium accumulation in rice (Oryza sativa L.)

Cadmium (Cd) contamination in paddy fields affects human health because of the consumption of Cd-contaminated rice. In the current study, we demonstrated that variation in root system architecture (RSA) influenced Cd uptake by rice. Rice cultivars consisting of KDML105, Mali Dang, Pitsanulok2 and Niaw San-pah-tawng were assessed in hydroponics and mesocosms while KDML 105, Pitsanulok2, and RD53 were used in field experiments. In hydroponics, root number and root weight were positively correlated with Cd uptake. In mesocosms, we found that the effects of Cd on RSA depended on rice varieties. Among different rice varieties, Mali Dang consistently accumulated high concentration of Cd, while Niaw San-pah-tawng tended to accumulate much lower amount in its shoot in both hydroponics and mesocosms. Correlation analysis indicates that Cd concentrations in shoot was positively correlated with root weight (R² = 0.95), crown root number (R² = 0.74), and negatively correlated with root depth (R² = 0.86). In the field, Cd is most abundant at a depth of 10-20 cm. and root distribution influenced Cd uptake as evidenced by high root Cd content in the RD53 variety. We propose that low crown root number and deep RSA could be promising traits for selection and breeding for low Cd uptake rice.

Aquatic plants for phytostabilization of cadmium and zinc in hydroponic experiments

Cadmium (Cd) may be toxic to aquatic plants even at modest concentrations, and excessive quantities of zinc (Zn) decrease plant performance. The Cd and Zn phytoremediation potential of several aquatic plant species (Thalia geniculate, Cyperus alternifolius, Canna indica, Eichhornia crassipes, Pistia stratiotes) and one grass species (Vetiveria zizanioides) was evaluated in hydroponic experiments. Vetiveria zizanioides, E. crassipes, and P. stratiotes experienced reduced growth performance in the presence of Cd as determined from biomass production, survival rate, and crown root number (CN); however, they accumulated high quantities of metals in their tissues, particularly in roots. Root accumulation is considered a key characteristic of so-called excluder species. In this study, only E. crassipes and P. stratiotes had bioconcentration factors and translocation factors (> 1000 and < 1, respectively) suitable for high phytostabilization of Cd. Furthermore, V. zizanioides and P. stratiotes showed the highest percent metal uptake from solution and removal capacity for Zn (~70% and ~2 mg d^-1 g^-1, respectively). Emergent aquatic species (particularly C. alternifolius and T. geniculate) adapted and lived well in Cd- and Zn-contaminated solution and took up high quantities of Cd and Zn in roots, and are therefore considered strong excluders. Beneficial uses of such species in contaminated wetlands include stabilizing toxic metals and limiting erosion. Plant tissue can be applied to other uses, including as a biomass fuel. In field situations, the candidate species may work best when grown together, since each plant genotype possesses a different potential to control Cd and Zn.

Synergistic phytoremediation of wastewater by two aquatic plants (Typha angustifolia and Eichhornia crassipes) and potential as biomass fuel

The ability of a mixture of Typha angustifolia and Eichhornia crassipes to remove organics, nutrients, and heavy metals from wastewater from a Thailand fresh market was studied. Changes in physicochemical properties of the wastewater including pH, temperature, chemical oxygen demand, dissolved oxygen, biochemical oxygen demand (BOD), total P, TOC, conductivity, total Kjeldahl nitrogen, NO₃^--N, NH₃-N, and metal (Pb, Cd, and Zn) concentrations were monitored. In the aquatic plant (AP) treatment, 100% survival of both species was observed. Dry biomass production and growth rate of T. angustifolia were approximately 3.3× and 2.7× of those for E. crassipes, respectively. The extensive root system of the plants improved water quality as determined by a marked decrease in turbidity in the AP treatment after 7 days. BOD content served as a useful indicator of water quality; BOD declined by 91% over 21 days. Both T. angustifolia and E. crassipes accumulated similar quantities of metals in both roots and shoots. Accumulation of metals was as follows: Zn > Cd > Pb. A study of calorific value and biomass composition revealed that T. angustifolia and E. crassipes possessed similar carbon content (~ 35%), hydrogen content (~ 6%), and gross calorific value. E. crassipes contained up to 16.9% ash and 65.4% moisture. Both species are considered invasive in Thailand; however, they may nonetheless provide practical benefits: In addition to their combined abilities to treat wastewater, T. angustifolia holds potential as an alternative energy source due to its high biomass production.

Phytomanagement of radionuclides and heavy metals in mangrove sediments of Pattani Bay, Thailand using Avicennia marina and Pluchea indica

This study determines uptake and accumulation of radionuclides and heavy metals by Pluchea indica and Avicennia marina and evaluates phytoremediation potential via greenhouse and field experiments. P. indica and A. marina are considered excluders for ⁴⁰K and ²⁶²Ra, and Pb since roots accumulated them in higher quantities compared to other plant parts, and the bioconcentration factor (BCF) and transfer factor (TF) values for Pb, and ⁴⁰K and ²⁶²Ra were >1, respectively. Absorbed dose rate in air (D) showed significant values in sediments, which were generally over the maximum recommended value of 55nGyh^-1. Phytostabilization of radionuclides and heavy metals may serve as an appropriate strategy for mangrove-polluted areas. D values in sediments were considered sufficiently high to recommend long-term monitoring. Radionuclide activities may increase in the food chain via uptake and accumulation of edible plants, ultimately resulting in harm to human health.

Influence of amendments on Cd and Zn uptake and accumulation in rice (Oryza sativa L.) in contaminated soil

Cadmium is a toxic metallic element that poses serious human health risks via consumption of contaminated agricultural products. The effect of mixtures of dicalcium phosphate and organic amendments, namely cow manure (MD) and leonardite (LD), on Cd and Zn uptake of three rice cultivars (KDML105, KD53, and PSL2) was examined in mesocosm experiments. Plant growth, Cd and Zn accumulation, and physicochemical properties of the test soils were investigated before and after plant harvest. Amendment application was found to improve soil physicochemical properties; in particular, soil organic matter content and nutrient (N, P, K, Ca, and Mg) concentrations increased significantly. The MD treatment was optimal in terms of increasing plant growth; the MD and LD treatments decreased soil Cd concentration by 3.3-fold and 1.6-fold, respectively. For all treatments, all rice cultivars accumulated greater quantities of Cd and Zn in roots compared with panicles and shoots. Among the three cultivars, RD53 accumulated the lowest quantity of Cd. Translocation factors (<0.28) and bioconcentration coefficients of roots (>1) indicate that the three rice cultivars are Cd excluders. Our results suggest that a mixture of organic and inorganic amendments can be used to enhance rice growth while reducing accumulation of heavy metals when grown in contaminated soil.

Occurrence of heavy metals and radionuclides in sediments and seawater in mangrove ecosystems in Pattani Bay, Thailand

Mangrove ecosystems in Pattani Bay, Thailand are considered representatives for monitoring the occurrence of anthropogenic and natural pollution due to metal and radionuclide contamination. Sediments and seawater were collected from five locations to determine metal (Cd, Cr, Cu, Mn, Ni, Zn, and Pb) and radionuclide (²²⁶Ra, ²³²Th, and ⁴⁰K) concentrations. Spatial variations in metal and radionuclide concentrations were determined among the sampling sites. A geoaccumulation index (I _geo ) and enrichment factor (EF) were used to classify the impacts of metals from anthropogenic point sources. Significant values for I _geo and EF were measured for Pb in site 4 (I _geo 0.65; EF 28.2) and Cd in site 1 (I _geo 1.48; EF 46.2). EF values in almost all sampling sites were >1 which indicates anthropogenic pollution. To assess the potential public hazard of radioactivity, the average radium equivalent activity (Ra_eq), the external hazard index (H _ex), the internal hazard index (H _in), the absorbed dose rate in air (D), and the annual effective outdoor dose rate (E) were determined. Based on these measurements, it is concluded that the probability of human health risk from radionuclides is low. However, the absorbed dose in air (D) values in sites 4 and 5 were greater than the global average value of 55 nGy h^-1, indicating that sediments in these locations pose a radiological hazard. The data obtained in this study provides useful information on metal and radionuclide background levels in mangrove sediments and seawater, and can be applied toward human health risk assessment and metal and radionuclide mapping.

Radionuclide (226Ra, 232Th, 40K) accumulation among plant species in mangrove ecosystems of Pattani Bay, Thailand

Little is known regarding phytoremediation of radionuclides from soil; even less is known about radionuclide contamination and removal in tropical ecosystems such as mangrove forests. In mangrove forests in Pattani Bay, Thailand, 18 plant species from 17 genera were evaluated for radionuclide concentrations within selected plant parts. Two shrub species, Avicennia marina and Pluchea indica, accumulated the highest ²³²Th (24.6Bqkg^-1) and ⁴⁰K (220.7Bqkg^-1) activity concentrations in roots, respectively. Furthermore, the aquatic species Typha angustifolia accumulated highest ²³²Th, ⁴⁰K and ²²⁶Ra activity concentrations (85.2, 363.5, 16.6Bqkg^-1, respectively) with the highest transfer factors (TFs) (3.0, 2.0, 5.9, respectively) in leaves. Leaves of T. angustifolia had an absorbed dose rate in air (D) over the recommended value (74.8nGyh^-1) that was considered sufficiently high to be of concern for human consumption.

Phytostabilization potential of two ecotypes of Vetiveria zizanioides in cadmium-contaminated soils: greenhouse and field experiments

Soil contamination by cadmium (Cd) poses a serious environmental and public health concern. Phytoremediation, i.e., the use of plants to remove contaminants from soil, has been proposed for treatment of Cd-contaminated ecosystems. In this study, we demonstrated the potential of Vetiveria zizanioides, commonly known as vetiver, to serve as an effective phytoremediation agent. Two ecotypes, i.e., India and Sri Lanka, were grown in greenhouse pots and in the field. Soils were amended with cow manure, pig manure, bat manure, and an organic fertilizer. Among all amendments, pig manure performed best in both greenhouse and field studies in terms of increasing total V. zizanioides biomass production in both ecotypes. In both greenhouse and in the field, tissue of the Sri Lanka ecotype had higher Cd concentrations than did the India ecotype. In the greenhouse, the presence of Cd did not affect total biomass production or root dry weight. The Sri Lanka ecotype had 2.7 times greater adventitious root numbers and 3.6 times greater Cd accumulation in roots than did the India ecotype. In the field study, the Sri Lanka ecotype offers potential as an excluder species, as it accumulated Cd primarily in roots, with translocation factor values <1 and a bioconcentration coefficient for roots >1 for all experiments except for the pig manure amendment. In addition, the highest Cd concentration in the Sri Lanka ecotype root (71.3 mg kg(-1)) was consistent with highest Cd uptake (10.4 mg plant(-1)) in the cow manure treatment. The India ecotype contained lower root Cd concentrations, and Cd accumulation was slightly higher in shoots compared to roots, with translocation factor (TF) values >1. The India ecotype was therefore not considered as an excluder in the Cd-contaminated soil. With the use of excluder species combined with application of organic amendments, soil contamination by Cd may be treated by alternative remediation methods such as phytostabilization.

Phytostabilization of a Pb-contaminated mine tailing by various tree species in pot and field trial experiments

The potential of 6 tree species (Leucaena leucocephala, Acacia mangium, Peltophorum pterocarpum, Pterocarpus macrocarpus, Lagerstroemia floribunda, Eucalyptus camaldulensis) for phytoremediation of Pb in sand tailings (total Pb >9850 mg kg(-1)) from KEMCO Pb mine in Kanchanaburi province, Thailand, were investigated employing a pot experiment (3 months) and field trial experiment (12 months). In pot study E. camaldulensis treated with Osmocote fertilizer attained the highest total biomass (15.3 g plant(-1)) followed by P. pterocarpum (12.6 g plant(-1)) and A. mangium (10.8 g plant(-1)) both treated with cow manure. Cow manure application resulted in the highest root Pb accumulation (>10000 mg kg(-1)) in L. floribunda and P. macrocarpus. These two species also exhibited the highest Pb uptake (85-88 mg plant(-1)). Results from field trial also showed that Osmocote promoted the best growth performance in E. camaldulensis (biomass 385.7 g plant(-1), height 141.7 cm) followed by A. mangium (biomass 215.9 g plant(-1), height 102.7 cm), and they also exhibited the highest Pb uptake (600-800 microg plant(-1)). A. mangium with the addition of organic fertilizer was the best option for phytostabilization of Pb-contaminated mine tailing because it retained higher Pb concentration in the roots.