Anionic surfactants (AS), represented by linear alkylbenzene sulfonates (LAS), are compounds that can change the interfacial tension of target solutions. They are widely used in various industrial fields, such as daily chemicals, metal processing, leather, textiles, petroleum and petrochemicals.    

LAS are a kind of common organic pollutant that play an important regulatory role in the succession of algal communities. Previous studies have found that LAS promoted the growth of Microcystis at low concentrations (≤ 10 mg/L) while inhibiting growth at high concentrations (≥ 20 mg/L). However, there are few reports referring to the distribution pattern of LAS in water bodies and its potential impact on the interspecies competition of Microcystis communities and the comprehensive toxicity of blooms.   

Recently, a research group led by Prof. LI Dunhai from the Institute of Hydrobiology (IHB) of the Chinese Academy of Sciences elucidated the regulatory effects, regulatory thresholds, and biological mechanisms of environmental concentrations of LAS on Microcystis bloom toxicity from the perspectives of photosynthesis, population competition, and microcystin (MCs) synthesis. This study was published in Water Research.   

The researchers conducted field investigations in Lake Taihu, and they found that the concentration of AS (mainly LAS) in the water surface microlayer (SML) reached 580 μg/L, higher than that in the lower layer.    

Since floating Microcystis blooms overlap in space with the high concentration of AS in SML, the researchers speculated that the impact of LAS on Microcystis blooms may have been severely underestimated in previous studies. The results showed that the regulatory effect of LAS on Microcystis bloom toxicity under suitable simulated growth conditions can be divided into four pathways according to the mechanism and threshold.    

The four pathways are LAS concentrations above 0.267 or 0.431 mg/L (depending on light conditions) selectively promoted the photosynthetic competitive advantage of toxic Microcystis, leading to its higher population proportion in the community; coculture experiments showed that LAS above 0.354 mg/L promoted toxic Microcystis to occupy the biomass advantage in the community; LAS concentrations above 0.5 mg/L induced the synthesis and release of MCs; and up to 2 mg/L LAS selectively inhibited the absorption and utilization of nutrients by nontoxic Microcystis and disrupted the structure of their photosynthetic system reaction centers, thereby promoting the dominance of toxic Microcystis and exacerbating the comprehensive toxicity of algal blooms.    

In terms of mechanism, compared with nontoxic Microcystis, toxic Microcystis can better resist LAS stress by dissipating excess light, maintaining an intact membrane structure and maintaining cellular homeostasis. Transcriptome sequencing suggested that the photosynthetic damage of nontoxic Microcystis might be attributed to the impacts of LAS on the absorption and assimilation of nitrogen, which finally resulted in the degradation of phycobilisomes.   

This study reveals the important ecological significance of anionic surfactants, which can provide new insights for the establishment of wastewater discharge standards and water quality safety management. 

(Editor: MA Yun)