Purpose

Texcoco saline lake in Mexico is an important habitat for over 300 species and recharges the Mexico City aquifer. Presently, it is on the verge of disappearance due to increasing anthropogenic pressure and comprises only a few wetland remnants. The impacts of human activities on these wetlands are unknown and uninvestigated. In this regard, this study investigates the degree of metal contamination in this ecosystem during the period of 2015–2018.

Materials and methods

Twenty-six sediment samples were collected from nine different wetlands of Texcoco Lake and examined for 17 metals (Al, Fe, Ca, Mg, Na, K, As, Ba, Cd, Co, Cr, Cu, Mn, Ni, Pb, Zn, and Hg) using atomic absorption spectroscopy. The degree of metal accumulation and its ecological risks were evaluated on the basis of several indicators (geoaccumulation index, enrichment factor, sediment quality guidelines, ecotoxicological values, and potential ecological risk index). Furthermore, co-occurrence via multivariate statistical techniques was employed using the measured metal concentrations to identify their possible sources.

Results and discussion

The Cd, Cu, Pb, Zn, and Hg sediment concentrations were higher in magnitude than the background North American shale composite values, suggesting their external origin in all studied sediments. According to the calculated enrichment factors and geoaccumulation index, the sediments were mostly contaminated with Cd and Hg. The sediment quality guidelines and ecotoxicological values together with the ecological risk index suggested probable adverse biological effects due to the presence of Cr, Cu, Ni, and Hg. Cadmium and Hg accounted for nearly 51 and 45% of the ecological threat in the sediments. Based on the knowledge about metal levels and co-occurrence in different matrices and the multivariate data analyses of the detected metal concentrations, we infer that the main sources of metals are as follows: (1) Solonchaks and Vertisol soil types (Ca, Mg, Na, and K); (2) urban-industrial effluents from surrounding municipalities and Mexico City (Cu, Pb, and Zn); and (3) industrial discharges of Xalostoc zone (Cd and Hg) near Texcoco.

Conclusions

Our results emphasize the impacts of unregulated discharges from municipal, industrial, and metropolitan zones of Mexico City and construction activities for the elevated metal concentrations in the wetland sediments of Texcoco Lake.

中文翻译：

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墨西哥前Texcoco盐湖湿地沉积物中金属污染及其生态风险的评估

目的

墨西哥的Texcoco盐湖是300多种物种的重要栖息地，可为墨西哥城的含水层补给水。目前，由于人为压力的增加，它正处于消失的边缘，仅包含少量湿地残留物。人类活动对这些湿地的影响尚不得而知。在这方面，本研究调查了该生态系统在2015–2018年期间的金属污染程度。

材料和方法

从Texcoco湖的9个不同湿地中收集了26个沉积物样品，并检查了17种金属（Al，Fe，Ca，Mg，Na，K，As，Ba，Cd，Co，Cr，Cu，Mn，Ni，Pb， Zn和Hg），使用原子吸收光谱法。根据几个指标（地积累指数，富集因子，沉积物质量准则，生态毒理学值和潜在生态风险指数）评估了金属积累的程度及其生态风险。此外，使用测得的金属浓度通过多元统计技术进行共现，以识别其可能的来源。

结果和讨论

Cd，Cu，Pb，Zn和Hg沉积物浓度的幅度高于北美北美页岩的背景合成值，表明它们是所有研究沉积物中的外源。根据计算得出的富集因子和地质富集指数，沉积物中大部分被镉和汞污染。沉积物质量指南和生态毒理学值以及生态风险指数表明，由于存在Cr，Cu，Ni和Hg，可能产生不利的生物学影响。镉和汞分别占沉积物中生态威胁的51％和45％。根据有关不同基质中金属含量和共存的知识以及对检测到的金属浓度的多变量数据分析，我们推断出金属的主要来源如下：（1）Solonchaks和Vertisol土壤类型（Ca，镁，钠和钾）；（2）周边城市和墨西哥城的城市工业废水（铜，铅和锌）；（3）Texcoco附近的Xalostoc区（Cd和Hg）工业排放。

结论

我们的结果强调了墨西哥城市政，工业和大都市区无节制排放的影响以及Texcoco湖湿地沉积物中金属浓度升高的建筑活动。