Probabilistic risk assessment of diuron and prometryn in the Gwydir River catchment, Australia, with the input of a novel bioassay based on algal growth

Rapid and Sensitive Detection of Water Toxicity Based on Photosynthetic Inhibition Effect

To achieve rapid and sensitive detection of the toxicity of pollutants in the aquatic environment, a photosynthetic inhibition method with microalgae as the test organism and photosynthetic fluorescence parameters as the test endpoint was proposed. In this study, eight environmental pollutants were selected to act on the tested organism, Chlorella pyrenoidosa, including herbicides (diuron, atrazine), fungicides (fuberidazole), organic chemical raw materials (phenanthrene, phenol, p-benzoquinone), disinfectants (trichloroacetonitrile uric acid), and disinfection by-products (trichloroacetonitrile). The results showed that, in addition to specific PSII inhibitors (diuretic and atrazine), other types of pollutants could also quickly affect the photosynthetic system. The photosynthetic fluorescence parameters (Fv/Fm, Yield, α, and rP) could be used to detect the effects of pollutants on the photosynthetic system. Although the decay rate of the photosynthetic fluorescence parameters corresponding to the different pollutants was different, 1 h could be used as an appropriate toxicity exposure time. Moreover, the lowest respondent concentrations of photosynthetic fluorescence parameters to diuron, atrazine, fuberidazole, phenanthrene, P-benzoquinone, phenol, trichloroacetonitrile uric acid, and trichloroacetonitrile were 2 μg·L⁻¹, 5 μg·L⁻¹, 0.05 mg·L⁻¹, 2 μg·L⁻¹, 1.0 mg·L⁻¹, 0.4 g·L⁻¹, 0.1 mg·L⁻¹, and 2.0 mg·L⁻¹, respectively. Finally, diuron, atrazine, fuberidazole, and phenanthrene were selected for a comparison of their photosynthetic inhibition and growth inhibition. The results suggested that photosynthetic inhibition could overcome the time dependence of growth inhibition and shorten the toxic exposure time from more than 24 h to less than 1 h, or even a few minutes, while, the sensitivity of the toxicity test was not weakened. This study indicates that the photosynthetic inhibition method could be used for rapid detection of the toxicity of water pollutants and that algae fluorescence provides convenient access to toxicity data.

Coupling relation between urbanization and ecological risk of PAHs on coastal terrestrial ecosystem around the Bohai and Yellow Sea

Urbanization, the ecological risks of polycyclic aromatic hydrocarbons (PAHs) to terrestrial ecosystems, and the complex relationship between them have drawn globally attention. In this paper, a comprehensive indicator system was calculated to illustrate the levels of urbanization in 20 coastal cities around the Bohai and Yellow Sea. The top three cities with high levels of urbanization were Tianjin > Qingdao > Dalian. The ecological risk of phenanthrene (Phe) was 52.0%; while the risk of fluoranthene (Flt) was 25.8%, and that of pyrene (Pyr), benzo[a]anthracene (Bap), fluorene (Flu), and naphthalene (Nap) were below 20% throughout the entire region. Risks were high in Dandong, Tianjin, Tangshan, Nantong, and Lianyungang and low in Weihai, Dongying, and Rizhao. The degree of coupling between urbanization and ecological risk of PAHs was above high (0.6) and more than 50% of the coordination degrees were slight unbalance [0.3, 0.5). Furthermore, redundancy analysis showed that the indicator aspects of industry, transportation, and population made great contribution to PAHs risk. Industry correlated to Low Molecular Weight (LMW) PAHs, while transportation correlated to High Molecular Weight (HMW) PAHs. To minimize risk, urbanization scale should be under acceptable level, or the structure of industry and transportation should be optimized.

Degradation of prometryn in Ruditapes philippinarum using ozonation: Influencing factors, degradation mechanism, pathway and toxicity assessment

In recent years, prometryn was utilized as watergrass remover in the aquaculture industry, resulting in the accumulated residual in the aquatic products. The present study focuses on the ozone degradation of prometryn in the Ruditapes philippinarum. The ozone concentration in water increased along with the injection time (60min). The contents of hydroxyl (·OH) and superoxide (O2·^-) radicals increased along with the ozone injection time. The effects of temperature, pH, prometryn initial concentration and ozone concentration on the removal efficiency of prometryn were evaluated. The maximum removal efficiency of 86.12% was obtained under the conditions of pH 7, prometryn initial concentration 0.05 mg/kg and the ozone concentration 4.2 mg/L at 28 °C for 30 min. Ion chromatography (IC) and Fourier transform infrared (FT-IR) spectroscopy results show that the S and N atoms in the outer layer of the triazine ring during the prometryn degradation process were oxidized and removed. A total of 30 intermediate compounds were identified using the gas chromatography-mass spectrometry (GC-MS) method. Combined with the IC and FT-IR results, three possible degradation pathways of prometryn were proposed. The prometryn was finally degraded into some small molecules with reduced toxicity by 63.16% for 120 min ozonization treatment. Overall, our work provides a novel approach for prometryn degradation in Ruditapes philippinarum, which can be extended for removing the residues of agricultural and veterinary drugs in other aquatic products.

Evaluation of amicarbazone toxicity removal through degradation processes based on hydroxyl and sulfate radicals

The herbicide amicarbazone (AMZ), which appeared as a possible alternative to atrazine, presents moderate environmental persistence and is unlikely to be removed by conventional water treatment techniques. Advanced oxidation processes (AOPs) driven by ^•OH and/or SO₄^•- radicals are then promising alternatives to AMZ-contaminated waters remediation, even though, in some cases, they can originate more toxic degradation products than the parent-compound. Therefore, assessing treated solutions toxicity prior to disposal is of extreme importance. In this study, the toxicity of AMZ solutions, before and after treatment with different ^•OH-driven and SO₄^•--driven AOPs, was evaluated for five different microorganisms: Vibrio fischeri, Chlorella vulgaris, Tetrahymena thermophila, Escherichia coli, and Bacillus subtilis. In general, the toxic response of AMZ was greatly affected by the addition of reactants, especially when persulfate (PS) and/or Fe(III)-carboxylate complexes were added. The modifications of this response after treatment were correlated with AMZ intermediates, which were identified by mass spectrometry. Thus, low molecular weight by-products, resulting from fast degradation kinetics, were associated with increased toxicity to bacteria and trophic effects to microalgae. These observations were compared with toxicological predictions given by a Structure-Activity Relationships software, which revealed to be fairly compatible with our empirical findings.

Combination of Logistic and modified Monod functions to study Microcystis aeruginosa growth stimulated by fish feed

The ecological health of aquaculture water is threatened by wasted fish feed and herbicides. In order to study the effect of prometryn and fish feed on Microcystis aeruginosa growth based on Monod and Logistic functions, four different concentrations of prometryn (0, 50, 100 and 200 μg L^-1) and two different dosages of fish feed (0.075 g, 0.15 g; d < 0.85 mm) were added into the culture medium, and the fish feed was the source of nitrogen and phosphorus in the MII medium. Results showed that Microcystis aeruginosa growth can be fitted well by Logistic and modified Logistic functions with 0-200 μg L^-1 prometryn (R² = 0.981-0.998 and R² = 0.989-0.999, respectively). With the same concentration of prometryn, the maximum algae density (N_max) of Microcystis aeruginosa calculated by both Logistic and modified Logistic functions increased with increasing dosage of fish feed and with the same dosage of fish feed, N_max declined with increasing concentrations of prometryn. Inhibition of prometryn on algae growth stimulated by fish feed is of double concentration-dependence, inhibition rates (I) are lower in 0.15 g fish feed medium than 0.75 g ones generally, implying that more nutrients can alleviate the stress caused by prometryn on algae. Derived formula for the specific growth rate, growth rate and inhibition rate using modified Logistic function agreed reasonably well with measured data. Jointly application of modified Monod and Logistic functions can better describe the relationship between specific growth rates and nutrients concentrations compared to combination of Monod and Logistic functions. In addition, equations for describing variations of nutrients concentrations (PO₄^3--P and NH₄⁺-N) with time were also derived based on both modified Monod and Logistic functions, which agree reasonably well with the measured data. In sum, the combination of modified Monod and Logistic functions provides a promising and robust method in studying algal growth stimulated by fish feed in incubator experiments.

Nationwide screening of surface water toxicity to algae

According to the European Water Framework Directive (WFD), chemical water quality is assessed by monitoring 45 priority substances. However, observed toxic effects can often not be attributed to these priority substances, and therefore there is an urgent need for an effect-based monitoring strategy that employs bioassays to identify environmental risk. Algal photosynthesis is a sensitive process that can be applied to identify the presence of hazardous herbicides in surface water. Therefore, the aim of this study was to employ an algal photosynthesis bioassay to assess surface water toxicity to algae and to identify the compounds causing the observed effects. To this purpose, Raphidocelis subcapitata was exposed to surface water samples and after 4.5 h photosynthetic efficiency was determined using PAM fluorometry. In this rapid high throughput bioassay, algal photosynthesis was affected by surface water from only one of 39 locations. Single compounds toxicity confirmation elucidated that the observed effect could be solely attributed to the herbicide linuron, which occurred at 110 times the EQS concentration and which is not included in the WFD priority substances list. In conclusion, applying the algal photosynthesis bioassay enables more efficient and effective assessment of toxicity to primary producers because it: (i) identifies the presence of herbicides that would be overlooked by routine chemical WFD monitoring, and (ii) avoids redundant chemical analyses by focusing only on (non-)target screening in samples with demonstrated effects.

Integrated regional ecological risk assessment of multiple metals in the soils: A case in the region around the Bohai Sea and the Yellow Sea

Methodology to quantify and distinguish the spatial distribution of the risks from multiple pollutants within the region was developed in this paper. An integrated quantitative risk assessment was conducted by utilizing a large amount of information available to explore spatial distribution of risk by single and multiple pollutants, and the magnitude of the overall risk from multiple pollutants based on the current concentrations of pollutants and toxicity data. Two target criteria levels - level I (NOEC/LOEC based) and level II (LC/EC/IC₅₀ based) - were employed, and thus, the regional and sub-regional risks were evaluated according to these two levels. The risk of multiple toxic metals (As, Cd, Cr, Hg and Pb) to a terrestrial ecosystem for the region around the Bohai Sea and the Yellow Sea were evaluated as a case. The total overall ecological risks from heavy metals in the region for level I and level II were 21.73% and 12.53%, respectively. The risks were ranked in the order of Cr > As > Pb > Cd > Hg with Cr posing the greatest ecological risk, which was 61.12% for level I. The top three cities according to the level II ecological risk were Cangzhou > Lianyungang > Panjin, while the top three cities of level I ecological risk were Cangzhou > Panjin > Lianyungang. This method provides a quantitative risk assessment with multiple and clear protection levels for risk management.

Removal of prometryn from hydroponic media using marsh pennywort (Hydrocotyle vulgaris L.)

The aquatic plant Hydrocotyle vulgaris was evaluated for its efficacy in removing prometryn from nutrient solution. Under optimized experimental conditions, up to 94.0% of the initial prometryn was removed from the hydroponic culture medium by H. vulgaris in 30 days. The concentration of prometryn decreased from the initial level of 0.55 ± 0.013 mg/L to 0.036 ± 0.001 mg/L at the end of the experimental period. The removal kinetics followed first-order kinetic equation (Ct = 0.4569e^-0.09t). Half-life (t_1/2) of prometryn was greatly shortened from 27.16 days (without plant) to 5.58 days (with H. vulgaris). Approximately 22% of the initial prometryn residue was found in H. vulgaris tissue, while 11.7% was degraded by the plant in 30 days. The metabolites of prometryn detected were 2,4-diamino-1,3,5-triazine (in the hydroponic culture medium) and 2,4,6-trihydroxy-1,3,5-triazine (in plant tissue) after 30 days. The results indicate that H. vulgaris can be used for phytoextraction of prometryn and could potentially be effective in removing other s-trazine pesticides from contaminated aquatic ecosystems.

Regional multi-compartment ecological risk assessment: Establishing cadmium pollution risk in the northern Bohai Rim, China

Ecological risk assessment (ERA) has been widely applied in characterizing the risk of chemicals to organisms and ecosystems. The paucity of toxicity data on local biota living in the different compartments of an ecosystem and the absence of a suitable methodology for multi-compartment spatial risk assessment at the regional scale has held back this field. The major objective of this study was to develop a methodology to quantify and distinguish the spatial distribution of risk to ecosystems at a regional scale. A framework for regional multi-compartment probabilistic ecological risk assessment (RMPERA) was constructed and corroborated using a bioassay of a local species. The risks from cadmium (Cd) pollution in river water, river sediment, coastal water, coastal surface sediment and soil in northern Bohai Rim were examined. The results indicated that the local organisms in soil, river, coastal water, and coastal sediment were affected by Cd. The greatest impacts from Cd were identified in the Tianjin and Huludao areas. The overall multi-compartment risk was 31.4% in the region. The methodology provides a new approach for regional multi-compartment ecological risk assessment.

Uptake of 2,4-bis(Isopropylamino)-6-methylthio-s-triazine by Vetiver Grass (Chrysopogon zizanioides L.) from Hydroponic Media

2,4-bis(Isopropylamino)-6-methylthio-s-triazine (prometryn) poses a risk to aquatic environments in several countries, including China, where its use is widespread, particularly due to its chemical stability and biological toxicity. Vetiver grass (Chrysopogon zizanioides L.) was tested for its potential for phytoremediation of prometryn. Vetiver grass was grown in hydroponic media in a greenhouse, in the presence of prometryn, with appropriate controls. Plant uptake and removal of prometryn from the media were monitored for a period of 67 days. The results showed that the removal of the prometryn in the media was expedited by vetiver grass. The removal half-life (t1/2) was shortened by 11.5 days. Prometryn removal followed first-order kinetics (Ct = 1.8070e(-0.0601t)). This study demonstrated the potential of vetiver grass for the phytoremediation for prometryn.