Heavy metals are well-known environmental pollutants due to their toxicity, persistence in the environment, and bioaccumulative nature. Their natural sources include weathering of metal-bearing rocks and volcanic eruptions, while anthropogenic sources include mining and various industrial and agricultural activities. Mining and industrial processing for extraction of mineral resources and their subsequent applications for industrial, agricultural, and economic development has led to an increase in the mobilization of these elements in the environment and disturbance of their biogeochemical cycles. Contamination of aquatic and terrestrial ecosystems with toxic heavy metals is an environmental problem of public health concern. Being persistent pollutants, heavy metals accumulate in the environment and consequently contaminate the food chains. Accumulation of potentially toxic heavy metals in biota causes a potential health threat to their consumers including humans. This article comprehensively reviews the different aspects of heavy metals as hazardous materials with special focus on their environmental persistence, toxicity for living organisms, and bioaccumulative potential. The bioaccumulation of these elements and its implications for human health are discussed with a special coverage on fish, rice, and tobacco. The article will serve as a valuable educational resource for both undergraduate and graduate students and for researchers in environmental sciences. Environmentally relevant most hazardous heavy metals and metalloids include Cr, Ni, Cu, Zn, Cd, Pb, Hg, and As. The trophic transfer of these elements in aquatic and terrestrial food chains/webs has important implications for wildlife and human health. It is very important to assess and monitor the concentrations of potentially toxic heavy metals and metalloids in different environmental segments and in the resident biota. A comprehensive study of the environmental chemistry and ecotoxicology of hazardous heavy metals and metalloids shows that steps should be taken to minimize the impact of these elements on human health and the environment.

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Environmental Chemistry and Ecotoxicology of Hazardous Heavy Metals: Environmental Persistence, Toxicity, and Bioaccumulation

The increase in awareness of the damage caused by synthetic materials on the environment has led to the development of eco-friendly materials. The researchers have shown a lot of interest in developing such materials which can replace the synthetic materials. As a result, there is an increase in demand for commercial use of the natural fiber-based composites in recent years for various industrial sectors. Natural fibers are sustainable materials which are easily available in nature and have advantages like low-cost, lightweight, renewability, biodegradability and high specific properties. The sustainability of the natural fiber-based composite materials has led to upsurge its applications in various manufacturing sectors. In this paper, we have reviewed the different sources of natural fibers, their properties, modification of natural fibers, the effect of treatments on natural fibers, etc. We also summarize the major applications of natural fibers and their effective use as reinforcement for polymer composite materials.

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Natural Fibers as Sustainable and Renewable Resource for Development of Eco-friendly Composites: A Comprehensive Review

The present review gives a brief account of the toxic effects of heavy metals on fish. In aquatic ecosystem, heavy metals are considered as the most important pollutants, since they are present throughout the ecosystem and are detectable in critical amounts. Heavy metals, such as mercury, cadmium, copper, lead and zinc are of the most important pollutants which effect aquatic environment and fish. They are extremely dangerous for the health of fish. Most of these metals are characterized by being accumulated in tissues, and lead to the poisoning of fish. These metals can effectively influence the vital operations and reproduction of fish; weaken the immune system, and induce pathological changes. As such, fish are used as bio-indictors, playing an important role in monitoring heavy metals pollution. Finally, some recommendations are given to treatment of different kinds of wastewaters, sewage and agricultural wastes before discharge into the aquatic systems. Also, enforcement of laws and legislations regarding the protection of aquatic environments must be taken into consideration.

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Use of Fish as Bio-indicator of the Effects of Heavy Metals Pollution

There has been a growing interest in utilizing fibers as reinforcement to produce composite materials. Scientists prefer thermoplastic polymeric matrices than thermosets due to the low production cycle, lower cost of processing and high reparability of thermoplastics. Fiber-reinforced thermoplastic matrix composites have gained commercial success in the semistructural and structural applications. Various fibers are widely used as reinforcement in thermoplastic polypropylene (PP) matrix to prepare composites. Mechanical properties of fiber-reinforced PP composites (FRPCs) are studied by many researchers and few of them are discussed in this article. Various fiber treatments, which are carried out to improve the fiber–matrix adhesion to get improved mechanical properties, are also discussed in this article. This article also focuses on coupling agents and fiber loading which affect the mechanical properties of FRPCs significantly.

Mechanical properties of polypropylene composites: A review

Recent advances in removal techniques of Cr(VI) toxic ion from aqueous solution: A comprehensive review

Chromium (VI) induced acute toxicity and genotoxicity in freshwater stinging catfish, Heteropneustes fossilis.

Jute fabrics (hessian cloth) reinforced polypropylene (PP) matrix composites (45 wt% fiber) were fabricated by compression molding. Jute fabrics were treated with 2-hydroxyethyl methacrylate (HEMA) using ultraviolet radiation in order to improve the mechanical properties of the composites. Concentration of HEMA, soaking time and radiation dose were optimized. It was found that 15% HEMA in methanol along with photoinitiator Darocur-1173 (2 %), 10 min soaking time and 20th pass of radiation rendered better performance. Urea of different concentrations (0.5–2 %) was incorporated with 15 % HEMA to monitor its effect on the properties and 1 % urea revealed the best results. For the improvement of the properties, jute fabrics were treated with potassium permanganate (KMnO4) solution in acetone of different concentrations (0.02, 0.03, 0.05, and 0.5 %) at different soaking times (1, 2, 3, and 5 min) before the composite fabrication. Optimized jute fabrics (jute fabrics treated with 0.03 % KMnO4) were again treated with HEMA (15 %) solution along with urea (1 %) and promising improvement of mechanical properties of the composites was observed. Scanning electron microscopy, water uptake, soil degradation and thermal aging of the treated and untreated composites were also performed.

Role of potassium permanganate and urea on the improvement of the mechanical properties of jute polypropylene composites

Human and ecological risks of metals in soils under different land-use types in an urban environment of Bangladesh

The objective of this study was to examine the toxicological effect of two major heavy metal pollutants, lead chloride (PbCl2) and cadmium chloride (CdCl2), in the freshwater climbing perch, Anabas testudineus. Fish were exposed to 1.0 and 2.0 mg/L both metals and histopathological changes in gill, kidney and liver tissues were studied. Major changes observed in gill tissue were epithelial lifting, proliferation of epithelial cells, fusion of secondary lamellae, hyperplasia and hypertrophy of mucous cells, and necrosis of epithelial cells. Cell necrosis, degenerated kidney tubules, congestion, lymphocytic infiltration and vacuolation were the major abnormalities observed in kidney tissue. The most conspicuous changes in liver were darker nucleoli, irregularly shaped hepatocytes with dilated blood capillaries, and focal as well as single necrosis. Fish specimens exposed to PbCl2 exhibited pronounced changes in all tissues examined compared with those exposed to CdCl2. It is evident from this study that hea...

Lead- and cadmium-induced histopathological changes in gill, kidney and liver tissue of freshwater climbing perch Anabas testudineus (Bloch, 1792)

The concentrations of organophosphate flame retardants (OPFRs) in the indoor air and dust were measured in 25 unoccupied cars in Japan. In the indoor air of the cars, most OPFRs were neither detected nor found at a concentration lower than the method quantification limit. The highest concentration (1500 ng m−3) was obtained for tris(1-chloro-2-propyl) phosphate (TCIPP). By contrast, many OPFRs were detected in the dust samples collected from the interior of the cars. TCIPP and tris(2-ethylhexyl) phosphate (TEHP) were present at the highest concentrations at 390 μg g−1 (in dust from car seats) and 640 μg g−1 (in dust from car floor mats), respectively. The highest median concentrations (35 μg g−1 for car seats, 53 μg g−1 for car floor mats) were obtained for tris(2-butoxyethyl) phosphate (TBOEP). According to the results of our exposure assessment, the typical exposures to OPFRs via inhalation in car cabins ranged from 9.0×10−4 to 7.8×10−1 ng kg-bw−1 day−1. The typical exposures to OPFRs via dust ingestion ranged from 9.2×10−4 to 8.8×10−1 ng kg-bw−1 day−1. We compared these results with the ref-erence doses for OPFRs and found that, based on cur-rent information about the toxicities of OPFRs, exposure to OPFRs in car cabins via inhalation and dust ingestion is unlikely to have adverse human health effects.

Md. Al-Mamun

Papers

Chromium (VI) induced acute toxicity and genotoxicity in freshwater stinging catfish, Heteropneustes fossilis.

Role of potassium permanganate and urea on the improvement of the mechanical properties of jute polypropylene composites

Human and ecological risks of metals in soils under different land-use types in an urban environment of Bangladesh

Lead- and cadmium-induced histopathological changes in gill, kidney and liver tissue of freshwater climbing perch Anabas testudineus (Bloch, 1792)

Organophosphate flame retardants in the indoor air and dust in cars in Japan.