Analysis of bacterial biodiversity and ecological risk evaluation of organophosphorus in Lianhuan Lake

PLOS One | https://doi.org/10.1371/journal.pone.0332712 September 26, 2025 7 / 20 toxicity of organophosphorus chemicals on fish, daphnia, and green algae in Lianhuan Lake. The structural information for each compound was entered into the software by specifying its chemical name or CAS number or by uploading a molecular structure diagram, and the calculation was initiated via the software’s submit function. A chemical’s semi-lethal concentration (LC50) value, which indicates the concentration at which 50% of test organisms perish after a specific amount of time—typically 48 or 96 hours—is a quantitative measure of the chemical’s toxicity. The concentration of a chemical that has a 50% maximum influence is known as the EC50. These two measures are frequently employed to evaluate acute toxicity. The CHV refers to the concentration of a substance that induces notable harmful effects in an organism during a prolonged toxicity test. Typically, it requires extended periods of exposure to evaluate the long-term harmful effects. Taking logarithms for the three indicators LC50, EC50, and CHV helps in data analysis and comparison, according to the research results of Li et al. [32]. The anticipated toxicity value in the Globally Harmonized System (GHS) is classified using the approach outlined in Table 4. This method is used to evaluate the toxicity of organophosphorus substances. 2.5.3 T.E.S.T. The CAS numbers of each target compound were entered into the T.E.S.T. to predict fish acute toxicity

(Fathead Minnow 96 h LC50) and bioconcentration factor (BCF) using the Consensus method; results were generated automatically by the software. BCF represents the ratio of the concentration of a chemical substance in an organism’s body to the concentration of the chemical substance in the environment after exposure to the environmental medium of the chemical substance (e.g., water, soil) and is used to assess the ability of a chemical substance to enrich in an organism. A high BCF value means that the chemical can accumulate in the organism and thus may pose a potential hazard to the organism and to other organisms through the food chain. The Registration, Evaluation, Authorization, and Restriction of Chemical Substances (REACH) stipulates that if the BCF value of a chemical substance is less than 2000, it means that the substance accumulates less in living organisms, is less likely to cause accumulation problems in the environment, and has less ecological risk. 2.5.4 RQ. Risk quotient assessment (RQ), originally proposed by the U.S. Environmental Protection Agency [33], is a methodology used to assess the potential risk of chemicals in the environment to ecosystems and human health (US EPA, 1989). It is calculated using the following formula: RQ = MEC PNEC (9) PNEC = LC50 OR EC 50 AF (10) RQSUM = ∑n i=1 RQi (11) Table 4. Concentration dependent toxic classification (mg/L). Class The Acute Toxicity The Chronic Toxicity Harmless lgLC50 or lgEC50 > 0 lgCHV > 0 Harmful −1 < lgLC50 or lgEC50 < 0 −1 < lgCHV < 0 Toxic −2 < lgLC50 or lgEC50 < −1 −2 < lgCHV < −1

Highly toxic lgLC50 or lgEC50 < −2 lgCHV < −2 https://doi.org/10.1371/journal.pone.0332712.t004