Copper-DOM Complexes Reveal Heavy Metal Pollution Patterns in Northwest Pacific Estuaries

Estuarine Water Quality and Seasonal Dynamics

Recent research examining large-scale estuaries across the north-west Pacific reveals critical insights into how copper interacts with dissolved organic matter, serving as an indicator of heavy metal pollution. The comprehensive study, published in Communications Earth & Environment, analyzed six major estuaries: Yangtze River Estuary (YRE), Yellow River Estuary (YER), Tumen River Estuary (TRE), Liao River Estuary (LRE), Hai River Estuary (HRE), and Changjiang River Estuary (CRE), along with Zhujiang River Estuary (ZRE).

Through sophisticated statistical analysis and fluorescence spectroscopy, scientists discovered distinct pollution patterns correlated with human activity intensity. The research demonstrates that copper-DOM complexation provides a sensitive method for assessing environmental degradation in these vital coastal ecosystems.

Water Quality Parameters Show Clear Geographical Patterns

The investigation revealed striking differences in water quality parameters across the studied estuaries. Temperature (TEMP) and dissolved oxygen (DO) exhibited inverse relationships with latitude, with TEMP showing a close negative correlation with DO (r = -0.920, p < 0.01), suggesting near-saturated oxygen conditions throughout the study area.

Notably, LRE and HRE demonstrated significantly higher levels of chemical oxygen demand (COD), biological oxygen demand (BOD), total phosphorus (TP), fluoride, and copper compared to the other four estuaries. The temporal distribution of these pollutants showed distinct patterns, with LRE experiencing peak concentrations in October, while HRE showed maximum levels in February., according to recent innovations

Principal Component Analysis (PCA) effectively traced latent factors affecting water quality, with two principal components explaining 96.20% of total variance. PC1 (71.09%) showed strong positive loadings on COD, BOD, and TP, indicating these parameters as primary indicators of anthropogenic impact.

DOM Fluorescence Reveals Pollution Sources

The examination of dissolved organic matter (DOM) using excitation-emission matrix (EEM) spectroscopy uncovered three distinct fluorescence patterns across the estuaries. TRE exhibited strong microbial-derived humic-like and fulvic-like fluorescence substances, while YRE showed prominent tryptophan-like fluorescence substances. The remaining estuaries (LRE, HRE, CRE, and ZRE) displayed complex profiles containing all three fluorescence types.

When researchers added copper(II) to DOM samples, they observed distinctive quenching patterns that varied by estuary. The PARAFAC analysis identified seven fluorescent components (C1-C7), each representing different organic matter sources:

• C1: Free amino acid-like substances associated with petroleum
• C2: Tryptophan-like substances from domestic sewage
• C3: D’tryptophan-like substances from wetland vegetation
• C4: Polycyclic aromatic hydrocarbon-like industrial pollutants
• C5 and C6: Microbial humic-like and fulvic-like substances
• C7: Terrestrial-derived humic-like substances

Copper Binding Characteristics Expose Pollution Vulnerability

The quenching efficiency analysis revealed how different DOM components interact with copper pollution. In TRE, C2-TRLF quenching efficiencies reached 87.87% at 120 μmol L of Cu(II), then stabilized at higher concentrations. YRE exhibited unique M-shaped quenching patterns for multiple components, suggesting complex competitive binding between copper and organic substituents of different molecular weights.

Perhaps most significantly, LRE and HRE consistently showed higher quenching efficiencies across multiple components as copper concentrations increased, providing indirect evidence of poorer water quality in these industrialized estuaries. The modified Stern-Volmer equation parameters (f and LogK) further confirmed these patterns, with higher stability constants (LogK) observed in more polluted estuaries.

Environmental Implications and Monitoring Applications

This research establishes copper-DOM complexation as a powerful tool for assessing heavy metal pollution in estuarine systems. The distinct fluorescence signatures and quenching behaviors provide fingerprints for different pollution sources, from petroleum exploitation to industrial discharge and domestic sewage., as as previously reported

The findings have significant implications for environmental monitoring and regulation. By understanding how copper interacts with different DOM components, researchers can develop more sensitive early-warning systems for heavy metal pollution and better track the effectiveness of pollution control measures in vulnerable coastal ecosystems.

The study underscores the urgent need for targeted pollution management strategies, particularly in heavily impacted estuaries like LRE and HRE, where industrial and anthropogenic activities have created complex pollution scenarios requiring comprehensive remediation approaches.

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