Arsenic Cadmium and Lead Concentrations in Sediment and Biota from Songkhla Lake: A Review

This article reviews the existing data on trace elements (Arsenic (As), Cadmium (Cd) and Lead (Pb)) in sediments and biota from Songkhla Lake, a shallow coastal lagoon in Southern of Thailand between 1998 and 2012. At present, the situation of those trace elements in sediments show moderate concentration levels for Cadmium and Lead. High levels for Arsenic have been found in the Outer Section of Songkhla Lake especially at the mouths of Samrong, U-Taphao and Phawong canals. The accumulation of trace elements in fish muscle tissue was well within limits for human consumption

Behaviour of heavy metals in a mud flat of the Scheldt estuary, Belgium

The Ballasplaat intertidal mud flat in the Scheldt estuary has been polluted by Cd and Pb and also high amounts of organic matter as a result of suspended matter deposition. The degree of pollution is, however, not uniform over the mud flat due to varying physico-chemical conditions (essentially variable redox profiles). Measurements of the redox profile, and the metal concentrations in the pore water, the total sediment and the fraction <63 µm combined with sequential extraction results and enrichment factors can explain the behaviour of Cd, Pb, Fe and Mn in the sediments. In a strong anoxic sediment, where sulphate reducing bacteria are active, the heavy metals are trapped as poorly soluble metal complexes while in an oxic or suboxic sediment metals tend to be redissolved due to the oxidation of organic matter, and the reduction of particulate Fe and Mn oxyhydroxides. The transportation of heavy metals across the sediment water interface is very much depending upon the physiochemical conditions of the sediment

Arsenic Cadmium and Lead Concentrations in Sediment and Biota from Songkhla Lake: A Review

AbstractThis article reviews the existing data on trace elements (Arsenic (As), Cadmium (Cd) and Lead (Pb)) in sediments and biota from Songkhla Lake, a shallow coastal lagoon in Southern of Thailand between 1998 and 2012. At present, the situation of those trace elements in sediments show moderate concentration levels for Cadmium and Lead. High levels for Arsenic have been found in the Outer Section of Songkhla Lake especially at the mouths of Samrong, U-Taphao and Phawong canals. The accumulation of trace elements in fish muscle tissue was well within limits for human consumption

Seasonal variations in sediment sulfur cycling in the Ballastplaat mudflat, Belgium

Sulfate reduction rate (SRR) and pools of reduced inorganic sulfur, acid volatile sulfide (AVS), chromium reducible sulfur (CRS), and elemental sulfur (So), were studied from June 1990 till March 1992 at two locations on the Ballastplaat mudflat in the Scheldt estuary. The sediment composition at station A was mainly sand with low organic content whereas sediments at station B were dominated by silt and clay with high organic content. SRR was positively related to temperature; more pronounced at station B (Ea=190 kJ mol-1) than at station A (Ea=110 kJ mol-1). The maximum SRR values observed equalled 14 µmol cm-3 d-1 at station B and 1 µmol cm-3 d-1 at station A. AVS was the dominant radiolabelled end product of the sulfate reduction reaction, except in surface sediments where pyrite and So were more dominant. However, CRS was the predominant reduced inorganic sulfur pool in the sediments. Both AVS and CRS pools showed temporal variations out of phase with SRR. SRR peaked in summer, while the concentrations of AVS and CRS were highest in fall. The accumulation of AVS and CRS started late summer after depletion of oxidants, which had accumulated during winter and spring. The estimated annual SRR and thus sulfide production in the upper 15 cm of station B was of the order of 100 mol m-2 yr-1, and at station A of the order of 12 mol m-2 yr-1. The sulfur mass balance shows that only a very small fraction, if any, of the produced sulfide is retained as reduced inorganic sulfur in the sediment

Overview of trace metal contamination in the Scheldt estuary and effect of regulatory measures

Seasonally, dissolved and particulate metal concentrations in the Scheldt estuary were assessed over a period of 4 years (1995–1998). High quality data were obtained following stringent analytical protocols for each step: sampling, sample treatment, sample storage and analysis. Of the 5 trace metals, Ni showed the most conservative behaviour, while Cd and Cu were clearly transferred from the particulate to the dissolved phase in the middle estuary. A substantial part of the particulate metals entering the estuarine system are lost through sedimentation. General seasonal patterns are the following: lower concentrations in spring and higher ones in winter (sometimes late fall/early winter) for dissolved metals, while in summer a pronounced rise of the longitudinal concentration profile is observed for the particulate metals. A comparison of the trace metal concentrations (dissolved and particulate) at the mouth of the estuary in 1995–1998 with those from 1981 to 1983, reveal reductions between 30 and 58%. Reductions based on direct emission measurements for almost the same period suggest reductions (dissolved + particulate) between 42 and 64%. Biomagnification (BMF) is the accumulation of a compound through the food-chain. It is in our case expressed as the ratio of the metal concentration in the organism (µg g–1, d.w.)/the metal concentration in total suspended matter (µg g–1, d.w.). Almost all BMF-values of Periwinkle, Nereis diversicolor and Macoma balthica (3 bottom organisms in the Scheldt estuary) are negative meaning that these organisms contain less heavy metals than the particulate suspended matter. For all organisms log BMFs for Pb, respectively Ni, are around –1.8, respectively –0.7. For Cd, Periwinkle shows slight enrichment (0.05) and for Cu even more (0.45), while negative values were observed for Nereis diversicolour and Macoma balthica. The latter organisms are more enriched in Zn (–0.09) than Periwinkle (–0.43)

Carbon and nitrogen cycling in intertidal sediments near Doel, Scheldt Estuary

Carbon and nitrogen cycling in intertidal mud flat sediments in the Scheldt Estuary was studied using measurements of carbon dioxide, methane and nitrous oxide emission rates and pore-water profiles of CO2, ammonium and nitrate. A comparison between chamber measured carbon dioxide fluxes and those based on CO2 pore-water gradients using Fick's First law indicates that apparent diffusion coefficients are 2 to 28 times higher than bulk sediment diffusion coefficients based on molecular diffusion. Seasonal changes in gaseous carbon fluxes or CO2 pore water concentrations cannot be used directly, or in a simple way, to determine seasonal rates of mineralization, because of marked seasonal changes in pore-water storage and exchange parameters.The annual amount of carbon delivered to the sediment is 42 mol m&#x2013;2, of which about 42% becomes buried, the remaining being emitted as methane (7%) or carbon dioxide (50%). Each year about 2.6 mol N m&#x2013;2 of particulate nitrogen reaches the sediment; 1.1 mol m&#x2013;2 is buried and 1.6 mol m&#x2013;2 is mineralized to ammonium. Only 0.42 mol m&#x2013;2 yr&#x2013;1 of the ammonium produced escapes from the sediments, the remaining being first nitrified (1.2 mol m&#x2013;2 yr&#x2013;1) and then denitrified (1.7 mol m&#x2013;2 yr&#x2013;1). Simple calculations indicate that intertidal sediments may account for about 14% and 30% of the total estuarine retention of nitrogen and carbon, respectively