Distribution and speciation of some metals in mangrove sediments from Jiulong river estuary, People's Republic of China

Dynamics and geochemical responses of dissolved metals (Mn and Cu) in a subtropical estuary, China

The research delved into the occurrence and dynamics of dissolved metals, specifically manganese (Mn) and copper (Cu), within the Jiulong River Estuary, South China, a medium-sized subtropical estuary. Our findings unveiled a nuanced seasonal and spatial variability of dissolved metals throughout the entire estuarine system. Notably, dissolved Mn concentrations peaked (~ 3.5 μM) in the upper estuary, diminishing sharply along the salinity gradient, with a modest rise in the middle estuary and outer Xiamen Bay. In the upper estuary, heightened concentrations of dissolved Mn occurred in spring due to augmented terrestrial particle inputs, followed by suboxically reductive releases; conversely, concentrations were low in summer, attributed to dilution from increased freshwater discharges and particle scavenging. In contrast, dissolved Cu exhibited differently, with elevated concentrations (29.2-37.5 nM) in the upper and middle estuaries, driven by reductive dissolution of Mn particles and chloride-induced ion exchanges, respectively. Concurrently, heightened inputs of nutrients and metals correlated with elevated phytoplankton productivity (indicated by chlorophyll a) in the upper and outer estuary regions. Our analysis underscored the sensitivity of dissolved metals to environmental parameters, including temperature, pH, and dissolved oxygen. The integration of compiled historical data underscored the dynamic nature of dissolved metals, particularly Cu, in response to geochemical processes.The elevated ion levels indicated intensified ion releases from particles and sediments, attributable to increased anthropogenic perturbation and climatic changes (e. g. ocean warming).

Halogenated organic pollutants in sediments and organisms from mangrove wetlands of the Jiulong River Estuary, South China

Eighteen sediments and four biota species were collected from mangrove wetlands of the Jiulong River Estuary (JRE) in South China to investigate the distribution of dichlorodiphenyltrichloroethane (DDT), polychlorinated biphenyls (PCBs), polybrominated diphenyl ethers (PBDEs), decabromodiphenyl ethane (DBDPE), dechlorane plus (DP) and 1,2-bis(2,4,6-tribromophenoxy)ethane (BTBPE). Concentrations of ΣDDTs, ΣPCBs, ΣPBDEs, DBDPE, DP, and BTBPE in mangrove sediments ranged from 21 to 84, 0.52-2.5, 9.0-66, 5.1-32, 0.05-0.14, and 0.03-0.25 ng/g dry weight, respectively. Levels of ΣDDTs, ΣPCBs, ΣPBDEs, DBDPE and DP in mangrove biota ranged from 950 to 30000, 56-400, 8.0-35, nd-20 and 0.44-3.1 ng/g lipid weight, respectively. DDTs were the predominant halogenated organic pollutants (HOPs) in mangrove sediments from the JRE, while PBDEs were the major HOPs in mangrove sediments from the Pearl River Estuary (PRE), suggesting that sediments in JRE and PRE had different sources of HOPs. The dominance of DDTs was found in both mangrove sediments and biota from the JRE, indicating that HOPs in JRE environment mainly come from agricultural sources. The biota-sediment accumulation factors for DDTs and PCBs were significantly higher than those of PBDEs, DBDPE and DP, suggesting high bioavailability of DDTs and PCBs in mangrove biota. Trophic magnification factors for DDTs, PCBs, PBDEs, and DP were 10.5, 3.00, 2.66 and 1.23, respectively, indicating their potential of biomagnification in mangrove food webs.

Effect of copper on the accumulation and elimination kinetics of fluoroquinolones in the zebrafish (Danio rerio)

Fluoroquinolones (FQs) have attracted wide concerns due to their pseudo-persistent and universal presence in natural water. Here we exposed zebrafish separately to two FQs (enrofloxacin (ENR) and ofloxacin (OFL)) in different copper (Cu) concentrations for 20 days (d) in a flow-through system, followed by a 11 d depuration period in clean water to investigate compound specific bioaccumulation and tissue distribution. Two FQs could accumulate in zebrafish, and the high concentration was observed in liver. Moreover, the levels of FQs in different treatment groups were higher than the corresponding control fish group. The uptake rates (k₁), elimination rates (k₂), BCF value, and half-lives (t_1/2) of FQs ranged from 0.02 to 3.28 d^-1, 0.01 to 0.97 d^-1, 0.33 to 109.33, 9.90 to 69.31 d, respectively. With Cu exposure concentration's increasing, k₁ values in three tissues (liver, skin and gill) obviously decreased. The exposure concentration affected the BCF value significantly, but didn't change their relative compositions in liver, gill, skin, and muscle after long time exposure. BCF values of ENR were always a little bit higher than those of OFL in almost all the tissues (liver, skin and gill) in the low Cu concentration treatments, whereas, in the high Cu concentration treatments the bioconcentration factors (BCF) values of ENR were lower than the values of OFL. The exposure of Cu played an important role in the FQs bioconcentration and BCF. These results are meaningful for improved understanding and prediction of the behavior and fate of metallic and antibiotics in aqueous environments.

Trace metal behavior in sediments of Jiulong River Estuary and implication for benthic exchange fluxes

Severe metal pollution due to industrial effluents releases has been documented in Jiulong River estuary, Southern China. However, integrated understanding of trace metal behavior in the sediment is lacking. In the present study, DGT (diffusive gradients in thin films) technique was employed together with sediment cores to study the porewater dynamics of trace metals as well as the benthic exchange fluxes from four sampling sites over three different months. The sedimentary environment showed distinct spatial and temporal variations due to effluent discharge and biological activities. Metal behavior was controlled by early diagenetic reactions below the interface, in suboxic layer and in deeper sediment. Precipitation as sulfides and adsorption onto Mn/Fe (hydr)oxides were important in scavenging trace metals. Estimated exchange fluxes at sediment-water interface in this estuary indicated that the overlying water was a major source for trace metals, whereas sediments could also be the source if surface remobilization (Mn/Fe reduction) dominated. Our results highlighted the impacts of both natural and anthropogenic processes on the source, fate and transformation of trace metals in this dynamic system.

Trace metal geochemistry in mangrove sediments and their transfer to mangrove plants (New Caledonia)

Because of their physico-chemical inherent properties, mangrove sediments may act as a sink for pollutants coming from catchments. The main objective of this study was to assess the distribution of some trace metals in the tissues of various mangrove plants developing downstream highly weathered ferralsols, taking into account metals partitioning in the sediment. In New Caledonia, mangroves act as a buffer between open-cast mines and the world's largest lagoon. As a result of the erosion of lateritic soils, Ni and Fe concentrations in the sediment were substantially higher than the world average. Whatever the mangrove stand and despite low bioaccumulation and translocations factors, Fe and Ni were also the most abundant metals in the different plant tissues. This low bioaccumulation may be explained by: i) the low availability of metals, which were mainly present in the form of oxides or sulfur minerals, and ii) the root systems acting as barriers towards the transfer of metals to the plant. Conversely, Cu and Zn metals had a greater mobility in the plant, and were characterized by high bioconcentration and translocation factors compared to the other metals. Cu and Zn were also more mobile in the sediment as a result of their association with organic matter. Whatever the metal, a strong decrease of trace metal stock was observed from the landside to the seaside of the mangrove, probably as a result of the increased reactivity of the sediment due to OM enrichment. This reactivity lead to higher dissolution of bearing phases, and thus to the export of dissolved trace metals trough the tidal action. Cu and Zn were the less concerned by the phenomenon probably as a result of higher plant uptake and their restitution to the sediment with litter fall in stands where tidal flushing is limited.

Phase partitioning of trace metals in a contaminated estuary influenced by industrial effluent discharge

Severe trace metal pollution due to industrial effluents releases was found in Jiulong River Estuary, Southern China. In this study, water samples were collected during effluent release events to study the dynamic changes of environmental conditions and metal partitioning among dissolved, particulate and colloidal phases controlled by estuarine mixing. Intermittent effluent discharges during low tide caused decreasing pH and dissolved oxygen, and induced numerous suspended particulate materials and dissolved organic carbon to the estuary. Different behaviors of Cu, Zn, Ni, Cr and Pb in the dissolved fraction against the conservative index salinity indicated different sources, e.g., dissolved Ni from the intermittent effluent. Although total metal concentrations increased markedly following effluent discharges, Cu, Zn, Cr, Pb were predominated by the particulate fraction. Enhanced adsorption onto particulates in the mixing process resulted in elevated partitioning coefficient (Kd) values for Cu and Zn, and the particle concentration effect was not obvious under such anthropogenic impacts. Colloidal proportion of these metals (especially Cu and Zn) showed positive correlations with dissolved or colloidal organic carbon, suggesting the metal-organic complexation. However, the calculated colloidal partitioning coefficients were relatively constant, indicating the excess binding capacity. Overall, the intermittent effluent discharge altered the particulate/dissolved and colloidal/soluble phase partitioning process and may further influence the bioavailability and potential toxicity to aquatic organisms.

Heavy metal and organic contaminants in mangrove ecosystems of China: a review

China's rapid economic growth has been accompanied by increasing environmental pollution. Mangrove ecosystems are now facing greater pollution pressures due to elevated chemical discharges from various land-based sources. Data on the levels of heavy metals and organic pollutants in mangrove compartments (sediments, plants, zoobenthos, and fish) in China over the past 20 years have been summarized to evaluate the current pollution status of the mangrove ecosystem. Overall, the Pearl River and Jiulong River estuaries were severely polluted spots. Concentrations of Cu, Zn, Cd, and Pb in mangrove sediments of Guangdong, Fujian, and Hong Kong were higher than those from Guangxi and Hainan. The pollution status was closely linked to industrialization and urbanization. The highest concentrations of polycyclic aromatic hydrocarbons (PAHs) were found in mangrove sediments from Hong Kong, followed by Fujian and Guangdong. Mangrove plants tend to have low-enriched ability for heavy metals and organic pollutants. Much higher levels of Pb, Cd, and Hg were observed in mollusks.

Variations of trace metals in two estuarine environments with contrasting pollution histories

In the present study, seasonal variations of metal concentrations were examined in two oyster species, Crassostrea hongkongensis and Crassostrea sikamea, and in seawater from a heavily contaminated estuary and a reference estuary. Strong temporal fluctuations of metal concentration were observed in oyster tissues as well as in seawater from both estuaries, especially for the contaminated estuary and for C. hongkongensis with higher accumulation ability. A closer inter-element correlation was observed for Cu, Zn, Cr and Ni in both the dissolved and particulate phases from the contaminated site, indicating that these metals originated from the same industrial sources. Seasonal variations of metals in oysters were not significantly related to their concentrations in seawater, but were related to the variations of condition index. Our results showed that the seasonal patterns of metal concentrations in oysters were largely controlled by the biological process, while the variation as well as the concentration were dependent on the contamination levels and bioaccumulation ability.

Phosphorus and cadmium interactions in Kandelia obovata (S. L.) in relation to cadmium tolerance

This study focused on the cadmium (Cd) tolerance of mangroves with application of phosphate (P) in order to explore whether exogenous P can alleviate Cd stress on these intertidal species. Kandelia obovata (S. L.) seedlings were cultivated in rhizoboxes under different levels of Cd and P concentrations. The speciation distributions of Cd in the rhizosphere and non-rhizosphere sediments were examined by sequential extraction procedures; organic acid in plant tissues and soil solution was measured by high-performance liquid chromatography; Cd and P accumulation in the plants was also determined. Results showed that considerable differences existed in Cd speciation distributions between rhizosphere and non-rhizosphere sediments. Root activity influenced the dynamics of Cd, P application increased the organic acid content in root tissues, P also increased Cd accumulation in roots whilst lowering Cd translocation from root to the above-ground tissues, and a significant positive correlation was found between Cd and P in roots (r = 0.905). It is postulated that Cd detoxification of K. obovata (S. L.) is associated with higher Cd immobilization in the presence of higher P and organic acid contents in root tissue.

Heavy-metal fractionation in surface sediments of the Cauvery River Estuarine Region, Southeastern coast of India

Geochemical fractionation of iron (Fe), manganese (Mn), copper (Cu), chromium (Cr), lead (Pb), zinc (Zn), and nickel (Ni) were determined using five-stage sequential extraction in sediments collected from estuarine stretches of Cauvery River delta on the eastern coast of India with emphasis on seasonal variation. Abundance of metals in terms of sum of total fractionations varied in the following order: Fe > Mn > Cr > Zn > Cu > Ni > Pb. Exchangeable fraction, believed to be bioavailable, showed differential abundances during the dry and wet seasons in the following order: Pb > Zn > Cu > Mn > Ni > Cr > Fe and Zn > Cu > Cr > Ni > Mn > Pb > Fe, respectively, indicating the possibility of anthropogenic influence. Among nonlithogenic fraction, organic matter-bound fraction is the second largest and a key scavenger for all of the heavy metals studied except Fe and Mn. A significant portion of Cu-associated organic matter fraction shows strong association of Cu with organic matter at most of the sampling sites. Environmental risk of metals evaluated using risk-assessment code and mobility factor showed low to high risk for Pb, Zn, and Cu. The results of the present study also hint at notable enrichment of heavy metals in the certain pockets of the Cauvery Estuary.

The short-term effect of cadmium on low molecular weight organic acid and amino acid exudation from mangrove (Kandelia obovata (S., L.) Yong) roots

The aim of this study was to evaluate short-term concentration and time effects of cadmium on Kandelia obovata (S., L.) Yong root exudation, thereby evaluating and predicting the ecophysiological effects of mangrove to heavy metals at the root level. Mature K. obovata propagules were cultivated in a sandy medium for 3 months, and then six concentrations of Cd (0, 2.5, 5, 10, 20, and 40 mg L(-1)) were applied. After exposure time of 24 h and 7 days, respectively, the root exudates of K. obovata were collected and low molecular weight organic acids (LMWOAs) and amino acids of which were analyzed. In addition, we measured glutathione, soluble protein content, and Cd concentration in the plant. We found 10 and 15 types of LMWOAs and amino acids in root exudates of K. obovata with total concentrations ranging from 29.54 to 43.08 mg g(-1) dry weight (DW) roots and from 737.35 to 1,452.46 ng g(-1) DW roots, respectively. Both of them varied in quality and quantity under different Cd treatment strengths and exposure times. Oxalic, acetic, L-malic, tartaric acid, tyrosine, methionine, cysteine, isoleucine, and arginine were dominant. Both LMWOAs and amino acids excreted from K. obovata roots play a key role in Cd toxicity resistance. The responsiveness of amino acids was less than that of LMWOAs. We suggest that the ecological effect of root-excreted free amino acids in the rhizosphere is mainly based on the role of nutrients, supplemented with detoxification to heavy metals.

Fate and effects of anthropogenic chemicals in mangrove ecosystems: a review

The scientific literature for fate and effects of non-nutrient contaminant concentrations is skewed for reports describing sediment contamination and bioaccumulation for trace metals. Concentrations for at least 22 trace metals have been reported in mangrove sediments. Some concentrations exceed sediment quality guidelines suggesting adverse effects. Bioaccumulation results are available for at least 11 trace metals, 12 mangrove tissues, 33 mangrove species and 53 species of mangrove-habitat biota. Results are specific to species, tissues, life stage, and season and accumulated concentrations and bioconcentration factors are usually low. Toxicity tests have been conducted with 12 mangrove species and 8 species of mangrove-related fauna. As many as 39 effect parameters, most sublethal, have been monitored during the usual 3 to 6 month test durations. Generalizations and extrapolations for toxicity between species and chemicals are restricted by data scarcity and lack of experimental consistency. This hinders chemical risk assessments and validation of effects-based criteria.

Metal concentrations in sediments of the Tamsui River, flows through central metropolitan Taipei

This work analyzed metal concentrations and potential sources of sediment pollutants in the Tamsui River, Taiwan, by instrumental neutron activation analysis. The Tamsui River, the second longest of Taiwan's three major rivers, flows through metropolitan Taipei City in northern Taiwan and is renowned for its preserved mangrove wetlands. In total 11 elements Al, As, Br, Cs, Fe, La, Mg. Mn, Na, Sc, and Ti were identified in 24 samples taken from three sites upriver, the mangrove area and estuary during the spring of 2004. Specifically, the most abundant Al metal concentration was 15.6-0.92 mg/g adopted as standard reference in this study. Only few sites had As at the statistical meaning (>DL). Furthermore, arsenic concentrations fluctuated at roughly 0.67 +/- 0.09 mg/kg based on variations in background counts in various gamma-ray spectra. Elemental concentrations of these elements were compared with those in other nations, and discussed in the context of enrichment factors calculated for elements using the earth crust of various sediments as references, based on elemental values of Al.

Distribution and mobility of copper, zinc and lead in plant-sediment systems of Quanzhou Bay estuary, China

The distribution, mobility and potential risks of Cu, Zn, and Pb in four typical plant-sediment co-systems of the Quanzhou Bay estuary wetland in southeast China were investigated using a sequential extraction procedure. The results show that the sediments were moderately or heavily contaminated with Zn and Pb in all four plant communities, and the plant-sediment systems could act as a sink for the heavy metals. In all investigated sediments, only a small proportion of measured heavy metals were distributed in exchangeable fraction and carbonate fraction, while the reducible fraction contained the highest amount of Zn and Pb of the total readily bioavailable fractions, and the oxidizable fraction exhibited a higher retention capacity for Zn and Cu, but lower for Pb. Alternanthera philoxeroides had the best ability to accumulate heavy metals among the four species. Phragmites communis was quite tolerant to Zn and Pb and had a good capability to transfer Zn and Pb. Aegiceras corniculatum seems to be effective in resisting heavy metal pollution, and therefore cannot serve as an indicator of contamination. The urgent need for many local enterprises is to carry out high-tech cleaner production to reduce the emission of pollutants and achieve a resource-economical and environment-friendly development.

Distribution and speciation of selected metals in surface sediments, from the tropical Zuari estuary, central west coast of India

Estuarine sediments are major reservoirs for the metals. Distribution and mobility of metals within estuaries depends strongly on their specific chemical form. In the present study, surface sediments from Zuari estuary, Goa were analysed by a sequential procedure for Fe, Mn, Cu, Zn, Cr and Co to determine their distribution in five geochemical phases (Exchangeable, carbonate, Fe-Mn oxide (reducible) organic bound (oxidisable) and residual). The total metal content, sand, silt, clay and organic carbon were also determined of the surface sediments. The total metal contents were found to be greater than the background concentrations of average shale values as well as to that of earlier studies indicating enrichment probably due to the anthropogenic origin of metals. The results obtained from sequential procedure showed that among the studied elements, Mn and Co are potentially available in the bioavailable fractions (exchangeable, carbonate and Fe-Mn oxide bound fractions) indicating their importance in toxicity whereas rest of the metals viz. Fe, Cu, Zn and to some extent Cr are largely available in residual phase although they are available in other fractions. The main source of metals to the estuary is mining and its associated activities in the study area. Chemical speciation by sequential extraction procedure has helped in assessing the mobility, bioavailability, diagenesis and toxicity of metals and hence giving a better insight into the ultimate fate of pollutants, which are introduced into the estuarine environment. To understand the risk of the metals to the sediment dwelling organisms the data were compared with the Sediment Quality Values (SQV) using SQUIRT. Also, correlation and Factor analysis were carried out to understand the associations of metals in the different fractions with sand, silt, clay, organic carbon and with other metals.

Effects of Cd and Zn on oxygen consumption and ammonia excretion in sipuncula (Phascolosoma esculenta)

Physiological responses (oxygen consumption and ammonia excretion) of the sipuncula (Phascolosoma esculenta) exposed to four concentrations of Cd (0.45, 0.96, 2.04, and 4.46 mg L(-1)) and four concentrations of Zn (1.09, 2.34, 4.96, and 10.91 mg L(-1)) were monitored for 21 days, respectively. Oxygen consumption rates of sipuncula at all concentrations of Cd decreased from day 1 to day 6. At low concentrations of Cd (0.45 and 0.96 mg L(-1)), the oxygen consumption rate was promoted. Time and concentration were significant in affecting oxygen consumption rate, respectively. Oxygen consumption rate decreased significantly with time for Zn-exposed individuals and also decreased significantly with the interaction between the concentration of Cd and time for Cd-exposed individuals. Changes occurred in the ammonia excretion rates and O:N ratios with individual sipuncula experiencing different metal concentrations over time. Although low O:N ratios (<30) were obtained in most of the treatments, no predictable correlation was found between concentrations of metals and values of O:N obtained. The value of using O:N ratio as a stress index is questioned.

Speciation changes of cadmium in mangrove (Kandelia candel (L.)) rhizosphere sediments

The speciation distribution of cadmium (Cd) in mangrove (Kandelia candel (L.) Druce) rhizosphere sediment was investigated after different contents of Cd being loaded. The study results indicated that root induced changes of Cd bioavailability in the rhizosphere. Exchangeable and carbonate bound Cd in the rhizosphere sediments were lower than these in the bulk sediments, whilst an increase in Fe-Mn oxides bound and O.M/sulfide bound fractions occurred in the rhizosphere sediment. Increased levels of Cd in sediments resulted in higher Cd concentrations in mangrove plants, and the order of accumulation was: roots > hypocotyls > stems and leaves.