Uptake and concentration of heavy metals in dominant mangrove species from Hainan Island, South China

Analysis of heavy metal and arsenic sources in mangrove surface sediments at Wulishan Port on Leizhou Peninsula, China, using the APCS-MLR model

Mangrove forests are sources and sinks for various pollutants. This study analyzed the current status of heavy metal and arsenic (As) pollution in mangrove surface sediments in rapidly industrializing and urbanizing port cities. Surface sediments of mangroves at Wulishan Port on the Leizhou Peninsula, China, were analyzed using inductively coupled plasma emission spectrometry (ICP-AES) and inductively coupled plasma mass spectrometry (ICP-MS) for the presence of Cr, Pb, Ni, Zn, Cd, Cu, As, and Hg. The Pollution load index, Nemerow pollution index, and Potential ecological risk index were employed to evaluate the pollutant. Multivariate statistical methods were applied for the qualitative analysis of pollutant sources, and the APCS-MLR receptor model was used for quantification. This study indicated the following results: (1) The average content of eight pollutants surpassed the local background level but did not exceed the Marine Sediment Quality standard. The pollution levels across the four sampling areas were ranked as Ⅲ > Ⅳ > Ⅰ > Ⅱ. The area Ⅱ exhibited relatively lower pollution levels with the grain size of the sediments dominated by sand, which was not conducive to pollutant adsorption and enrichment. (2) The factor analysis and cluster analyses identified three primary sources of contamination. As, Cr, Ni, and Pb originated from nearby industrial activities and their associated wastewater, suggesting that the primary source was the industrial source. Cd, Cu, and Zn stem from the cement columns utilized in oyster farming, alongside discharges from mariculture and pig farming, establishing a secondary agricultural source. Hg originated from ship exhaust burning oil and vehicle emissions in the vicinity, representing the third traffic source. (3) The APCS-MLR receptor model results demonstrated industrial, agricultural, and traffic sources contributing 47.19 %, 33.13 %, and 13.03 %, respectively, with 6.65 % attributed to unidentified sources.

Pb contaminated soil from a lead-acid battery plant immobilized by municipal sludge and raw clay

Soil heavy metal pollution poses a serious threat to the eco-environment. Municipal sludge-based passivators and clay minerals have been widely applied to immobilize heavy metal contamination in soils. However, little is known about the immobilization effect and mechanisms of raw municipal sludge and clay in reducing the mobility and bioavailability of heavy metals in soils. Here, municipal sludge, raw clay and mixtures of thereof were used to remediate Pb-contaminated soil from a Pb-acid battery factory. The remediation performance was evaluated through acid leaching, sequential extraction, and plant assay. Results showed that the leachable Pb content in the soil decreased from 5.0 mg kg-1 to 4.8, 4.8 and 4.4 mg kg-1 after 30 d of remediation with MS and RC added at equal weights to give total dosage of 20, 40 wt% and 60 wt %, respectively. The leachable Pb further decreased to 1.7, 2.0 and 1.7 mg kg-1 after 180 d of remediation. Speciation analysis of the soil Pb indicated that the exchangeable and Fe-Mn oxide-bound Pb were transformed into residual Pb in the early stage of remediation, and the carbonate-bound Pb and organic matter-bound Pb were transformed into residual Pb in the later stage of remediation. As a result, Pb accumulation in mung beans decreased by 78.5%, 81.1% and 83.4% after 180 days of remediation. These results indicate that the leaching toxicity and phytotoxicity of Pb in remediated soils were significantly reduced, presenting a better and low-cost method for soil remediation.

Combined Remediation Effects of Sewage Sludge and Phosphate Fertilizer on Pb-Polluted Soil from a Pb-Acid Battery Plant

Pb soil pollution poses a serious health risk to both the environment and humans. Immobilization is the most common strategy for remediation of heavy metal polluted soil. In this study, municipal sewage sludge was used as an amendment for rehabilitation of Pb-contaminated soils, for agricultural use, near a lead-acid battery factory. The passivation effect was further improved by the addition of phosphate fertilizer. It was found that the leachable Pb content in soils was decreased from 49.6 mg kg-1 to 16.1-36.6 mg kg-1 after remediation of sludge for 45 d at applied dosage of municipal sewage sludge of 4-16 wt%, and further decreased to 14.3-34.3 mg kg-1 upon extension of the remediation period to 180 d. The addition of phosphate fertilizer greatly enhanced the Pb immobilization, with leachable Pb content decreased to 2.0-23.6  mg kg-1 with increasing dosage of phosphate fertilizer in range of 0.8-16 wt% after 180 d remediation. Plant assays showed that the bioavailability of Pb was significantly reduced by the soil remediation, with the content of absorbed Pb in mung bean roots decreased by as much as 87.0%. The decrease in mobility and biotoxicity of the soil Pb is mainly attributed to the speciation transformation of carbonate, Fe-Mn oxides and organic matter bound Pb to residue Pb under the synergism of reduction effect of sludge and acid dissolution and precipitation effect of phosphate fertilizer. This study suggests a new method for remediation of Pb-contaminated soil and utilization of municipal sewage sludge resources.

Per- and polyfluoroalkyl substances in a subtropical river-mangrove estuary-bay system

Mangrove estuaries are one of the most economically valuable and biologically diverse coastal ecosystems. However, knowledge of emerging pollutants in mangrove estuaries is limited. This study provided insight into the PFAS in a river (Zhangjiang River, ZR)-mangrove estuary (Zhangjiang River Estuary, ZRE)-bay (Dongshan Bay, DSB) continuous system in Fujian Province, China. The Σ25PFAS (sum of 25 PFAS) concentrations (0.94 ∼ 62.44 ng/L) showed a declining trend from the river to bay. The Zhe-Min Coastal Current (ZMCC) can transport an abundance of PFAS, especially PFOA, from the northern sea to southern bays, which can affect the seasonal distribution of PFAS concentrations in the DSB and result in PFOA/Σ25PFAS with a decreasing trend in the DSB (28.08%), ZRE (21.15%), and ZR (14.13%), respectively. The primary PFAS sources in this area determined by the positive matrix factor model mainly contained the effluent of the wastewater treatment plant neighboring the R2 site, discharge of domestic and production wastewater, irregular emissions of aqueous film-forming foams, and fluorochemistry industry wastewater transmitted from the ZMCC. The PFAS pollution in the mangrove creek was mainly affected by the discharge of domestic and production wastewater and presented a significant point source pollution, especially during the rainy season.

Distribution, sources and ecological risks of per- and polyfluoroalkyl substances in overlying water and sediment from the mangrove ecosystem in Hainan Island, China

Since data on Per- and polyfluoroalkyl substances (PFASs) in mangrove ecosystems are very limited. This study investigated the occurrence, distribution, sources, and ecological risk of 24 PFASs in the overlying waters and sediments of mangrove systems in Hainan Island, China. The concentration levels of PFASs in water and sediment ranged from 6.3 to 35.3 ng/L and from 0.33 to 10.2 ng/g dw, respectively. In terms of spatial distribution, firstly, the mangrove forests in Haikou and Sanya contained higher levels of PFASs; secondly, the eastern region contained higher levels of PFASs than the western region. The reasons for this may be related to the population size and development level of the region. For the organic carbon normalized sediment-water partition coefficient (log Koc), the results showed that log Koc decreased with increasing carbon chains for short-chain PFASs (with ≤6 CF2 units) and increased with increasing carbon chains for long-chain PFASs (with ˃6 CF2 units). Principal Component Analysis (PCA) and correlation analysis were employed to pinpoint specific origins of PFASs, namely firefighting, metal plating, food packaging, textiles, and fluoropolymer manufacturing. The risk quotient (RQ) values of PFASs in mangrove ecosystems on Hainan Island were all <1, but the existence of potential risks cannot be excluded. Hence, further investigations related to the bioaccumulation effects of PFASs in organisms in mangrove forests should be conducted to gain a more comprehensive understanding of their environmental behavior.

Assessment of native plants for their potential to remove trace metals around Legadembi tailings dam, Southern Ethiopia

Native plant species growing on metal contaminated soil at the foot of the Legadembi tailings dam were selected to evaluate their phytoremediation potential. For this purpose, soil, aboveground tissues, and roots of plant samples were analyzed for the concentrations of Zn, Cu, Ni, Pb, and Cd. The bioaccumulation and transfer of metals were evaluated in terms of translocation factor (TF), bioconcentration factor (BCF), and biological accumulation coefficient (BAC). The results showed that most of the species were efficient to take up and translocate more than one trace element (TE) from roots to shoots. Argemone mexicana L., Rumex nepalensis Spreng., Cyperus alopecuroides Rottb., and Schoenoplectu sconfusus (N.E.Br.) Lye showed potential for phytoextraction of Cu, while R. nepalensis and C. alopecuroides can accumulate in their above-ground parts and are suitable for phytoextraction of Ni. Rumex nepalensis, C. alopecuroides, and Typha latifolia L. have the ability for phytostabilization of Zn metal. Findings suggest concentrations of some metals in plants' tissue showed above the normal range which suggests their potential use in phytoremediation.

An eco-sustainable approach towards heavy metals remediation by mangroves from the coastal environment: A critical review

Mangroves provide various ecosystem services, carbon sequestration, biodiversity depository, and livelihoods. They are most abundant in marine and coastal ecosystems and are threatened by toxic contaminants like heavy metals released from various anthropogenic activities. However, they have significant potential to survive in salt-driven environments and accumulate various pollutants. The adverse effects of heavy metals have been extensively studied and recognized as toxic to mangrove species. This study sheds light on the dynamics of heavy metal levels, their absorption, accumulation and transport in the soil environment in a mangrove ecosystem. The article also focuses on the potential of mangrove species to remove heavy metals from marine and coastal environments. This review concludes that mangroves are potential candidates to clean up contaminated water, soil, and sediments through their phytoremediation ability. The accumulation of toxic heavy metals by mangroves is mainly through roots with limited upward translocation. Therefore, promoting the maintenance of biodiversity and stability in the coastal environment is recommended as an environmentally friendly and potentially cost-effective approach.

Response of bacterial diversity and community structure to metals in mangrove sediments from South China

Human activities have given rise to metal contamination in the constituents of mangrove ecosystems, posing a critical threat to sediment microorganisms; hence, it is of great importance to comprehend the effects of metals on the microbial communities in mangrove sediments. This study was the first to explore the response of the bacterial diversity and community structure to nine metals (As, Co, Cr, Cu, Mn, Ni, Pb, V and Zn) and organic matter fractions (including total organic carbon (TOC), total nitrogen (TN), and total sulfur (TS)) in mangrove wetlands from Zhanjiang, China, using 16S rRNA high-throughput sequencing technology and Spearman correlation analysis. The results showed that these nine metals were scattered differently in different mangrove sediments, and the metals and organic matter fractions jointly affected the bacterial communities in the sediments. Several metals displayed significant positive correlations with the abundances of the phylum Bacteroidetes and the genera Actibacter and Sphingobacterium but significant negative correlations with the abundances of two genera Holophaga and Caldithrix. Furthermore, the abundances of the phylum Actinobacteria and many bacterial genera showed significant positive or negative responses to the levels of the three organic matter fractions. Interestingly, the levels of a number of bacterial genera that exhibited increased abundance with high levels of metals and TS might be reduced with high TOC and TN, and vice versa: the levels of genera that exhibited decreased abundance with high levels of metals and TS might be increased with high TOC and TN. Overall, many bacterial groups showed different response patterns to each metal or organic matter fraction, and these metals together with organic matter fractions influenced the bacterial diversity and community structure in mangrove sediments.

Accumulation of nutrients and potentially toxic elements in plants and fishes in restored mangrove ecosystems in South China

Mangroves are highly dynamic ecosystems that offer important services such as maintaining biodiversity, filtering pollutants, and providing habitats for fishes. We investigated the uptake and accumulation of nutrients and potentially toxic elements in mangrove plants and fish to better understand the role of mangrove restoration in maintaining mangrove biota quality. In mangrove plants, the average bioconcentration factors of nutrients and potentially toxic elements were in the order P > Pb > Mn > Mg > Se > Zn > Hg > Cu > Cd > As > Co > Cr > Ni > Fe > V > Sb, where only P (all plant species) and Pb (Sonneratia apetala Buchanan-Hamilton) had a BCF > 1.0 in mangrove plants. In general, Sonneratia spp. had better performances than Kandelia candel (Linn.) Druce, Aegiceras corniculatum (Linn.) Blanco and Acanthus ilicifolius L. Sp. in terms of nutrient uptake and toxic metal(loid)s accumulation, and the best uptake capacity was found in S. apetala. Fast growth and easy adaptation make S. apetala suitable for a restored mangrove ecosystem, but continual management is needed to prevent its suppression of mangrove species diversity. The concentration of As, Cd, Hg, Cu, Cr and Pb in the mangrove sediment were 30-220% higher than the Chinese National Standard of Marine Sediment Quality Class I limits, suggesting that the sediments were unsuitable for aquaculture and nature reserves. Although a higher toxic metal(loid)s concentration in the sediment was found, the target hazard quotient (THQ) of this toxic metal(loid)s in 5 mangrove habitat fishes was <1.0, except THQ of Pb in Boleophthalmus pectinirostris Linnaeus was 1.17, and THQ of Cr in Bostrychus sinensis Lacépède was 1.12. The low THQ (less than 1.0) of mangrove habitat fishes suggested that the restored mangrove system could alleviate the bioaccumulation of toxic metal(loid)s in mangrove fish.

Evaluation of the Development Potential of Hainan Free Trade Port Industrial Chain Driven by the Internet of Things Distribution Mechanism

This paper starts from the industrial structure and characteristics of the Internet of Things and compares and analyzes the development ideas of the Internet of Things industry in the market economy under different systems. We also discuss IoT business model innovations and analyze the inadequacies of current IoT business models. We use the cost-benefit analysis method to analyze, from the aspects of social benefits, economic benefits, environmental benefits, and externalities. In this paper, factor analysis and quantitative statistics are used to calculate the weight of influencing factors, and the multilevel fuzzy evaluation method is used to score the influencing factor indicators to calculate the final score result, so as to judge the applicability of the multilevel fuzzy evaluation method to judge the profit model. In order to verify whether the establishment of economic regions plays a positive role in regional economic development, a double-difference model is established. Two sets of data from the Free Trade Zone and Hainan Free Trade Zone are selected for regression analysis, and robustness tests of various methods are carried out. This paper regresses various samples of the Hainan Free Trade Zone by region and city level to explore their characteristics in different regions. From the empirical results, it can be seen that the establishment of the Hainan Free Trade Zone has indeed promoted the economic development of the region where it is located, and this result is still significant after repeated robustness tests. Judging from the regression results by region, the establishment of the Hainan Free Trade Zone has a greater role in promoting the economic development of the eastern and western regions and it has a stronger pulling effect on the western regions than in the western regions. The policy effect of establishing a free trade zone may not be significant due to too few samples and short establishment time.