Species, Spatial-Temporal Distribution, and Contamination Assessment of Trace Metals in Typical Mariculture Area of North China

Abstract

The species, spatial-temporal distribution, sources, correlations with physiochemical factors, and the contamination of trace metals (Cu, Pb, Cd, and Zn) were investigated in a typical mariculture area of North China. The concentrations of three species of trace metals, including total dissolved, dissolved reactive, and dissolved inert, were obtained. The total dissolved concentrations of Cu, Pb, Cd, and Zn ranged within 1.75-8.08, 0.43-2.75, 0.07-0.29, and 2.58-30.28 µg/L, respectively. These ranges were measured over 5 months (March, May, July, September, and November) and their concentrations decreased in the following order: Zn > Cu > Pb > Cd. The concentrations of Cu, Pb, Cd, and Zn decreased from nearshore to offshore, showing a distinctly regional variation. All concentrations of trace metals over the whole mariculture area were lower than the grade-II seawater quality standard of China. The relationships between trace metals with micronutrient metal (Fe) and other environmental factors (i.e., temperature, chlorophyll a, salinity, dissolved oxygen, and conductivity) were studied in detail. Discharged industrial and aquaculture effluents, uptake by organisms, and atmospheric deposition were found to be possible sources of trace metals in the studied area. Sea current and physicochemical parameters were factors that possibly influenced the spatial-temporal distribution of trace metals.

Concentration, Spatial-Temporal Distribution, and Bioavailability of Dissolved Reactive Iron in Northern Coastal China Seawater

“…Table 2 lists the average levels and the range of different species of iron over the five monitoring months in 2018. TdFe levels provided by our previous work ranged from 27.8 to 82.0 nM with decreasing values in March, November, September, July, and May [29], and DrFe content ranged from 6.8 to 13.3 nM with decreasing values in September, May, July, March, and November, the proportion of DrFe to TdFe ranging from 10.4% to 47.7%. As shown in Figures 3A,B and 4, DrFe changed little, while the variation trend of TdFe was opposite to and the proportion of DrFe to TdFe.…”

“…DrZn and DrCd followed similar trends, with relatively low concentrations in July and September. The variations in the dissolved reactive metal concentrations (DrCu, DrPb, DrCd, DrZn) were similar to that of total dissolved metals (TdCu, TdPb, TdCd, TdZn) [29]; this may be because the mean percentages of DrCu, DrPb, DrCd, and DrZn were almost greater than 60%. Because of the lack of significant correlation, the interaction between iron, these four metals, and other biogeochemical processes in Sishili Bay needs to be deeply studied with further investigation in the future.…”

“…Cu, Pb, Cd, and Zn are essential metals for the growth of organisms in marine environments but are also the main elements causing marine metal pollution. Dissolved reactive metals (DrCu, DrPd, DrCd, DrZn) were also detected previously in our team by anodic stripping voltammetry (ASV) in filtered seawater without any reagents [29]. Because of this, it is of vital importance to explore the relationships between the different reactive metal elements.…”

“…The physical and chemical parameters of seawater were measured using a YSI ProPlus Multiparameter Water Quality Measuring Instrument (Proplus, Dublin, Ireland). The concentration of Chl a was determined using a Turner Designs Trilogy fluorimeter, following the detailed steps described in a previous study by our team [29]. The concentrations of nitrates and phosphates were determined using flow injection analysis (QuAAtro, Bran+Luebbe, Hamburg, Germany).…”

“…Little research has focused on trace metals, especially metal speciation, in seawater from Sishili Bay. By using electrochemical methods (ASV), our team has studied the different morphology and distribution of four metals (Cu, Pb, Cd, and Zn) in this area [28,29]. Compared with other trace metals, iron is harder to determine due to its low concentration and electrochemical instability in seawater; however, as iron plays an important role in marine primary productivity, it is important to study the distribution and speciation of iron in Sishili Bay to understand further the geochemical processes occurring in coastal waters.…”