Effect of insecticides on soil algal population

Validation of the paper-disc soil method using soil alga Chlorococcum infusionum to quantitatively determine the toxicity of heavy metals

The paper-disc soil method is a soil algal bioassay used to assess soil water transfer in polluted soils. Although this ecotoxicological method was first established in 2016 to assess soil pollution, quantitative toxicity assessments of Cu- or Ni-treated soil and in situ or ex situ soils polluted with other heavy metals (HMs) have not been widely conducted. In this study, the paper-disc soil method was validated under different test conditions. The validated paper-disc soil method was used to quantitatively investigate the toxicity of four HMs (As, Cd, Cr, and Zn). Based on the results, the test species, initial inoculation concentration in the algal-dispersed solution, water content, light intensity, and exposure duration were proposed as Chlorococcum infusionum, 3 × 10⁶ cells/mL in Bold's basal medium, 80% water-holding capacity, 4000 ± 500 lx, and 6 days, respectively. The toxicity of HMs was quantified using the validated paper-disc soil method, and the half-maximal effective concentration values for biomass were calculated as 22.49 (21.26-23.78) mg Cr/kg dry weight (dw) soil, 42.72 (38.64-47.24) mg Cd/kg dw soil, 57.79 (55.46-60.21) mg As/kg dw soil, and 183.06 (175.38-191.06) mg Zn/kg dw soil. The paper-disc soil method using the soil alga C. infusionum was validated by quantitatively evaluating the test conditions and toxicity of HMs. Our results provide important quantitative toxicity data for soil algae exposed to HMs and a basis for standardizing the paper-disc soil method using soil algae.

Quantitative assessment of photosynthetic activity of Chlorella (Class Trebouxiophyceae) adsorbed onto soil by using fluorescence imaging

In the present study, we evaluate our previously developed non-destructive soil algal toxicity method using species from a different class of algae; Class Trebouxiophyceae (Chlorella vulgaris and Chlorella sorokiniana), and directly measure the photosynthetic activity of these species adsorbed onto the soil as a new toxicity endpoint. This study shows that non-destructive soil algal toxicity method is applicable to non-specific test species, including those of Class Trebouxiophyceae as well as Class Chlorophyceae (Chlorococcum infusionum and Chlamydomonas reinhardtii). Furthermore, by performing photosynthesis image analysis, we verify that it is possible to measure the photosynthetic activity of soil algae Chlorella vulgaris adsorbed onto soils without the need to extract algal cells from the soil. We propose that the non-destructive soil algal toxicity method represents a novel technique for 1) evaluating pollutants in soil using non-specific algae and 2) conveniently and rapidly assessing the photosynthetic activity of soil algae Chlorella vulgaris adsorbed onto soil as a new toxicity endpoint.

Assessing applicability of the paper-disc method used in combination with flow cytometry to evaluate algal toxicity

Soil algal bioassays have been limited by their inability to evaluate several toxic endpoints because it is difficult to collect pure soil algae growing on and beneath the soil surface. This study describes the extension of a previously developed paper-disc method for analyzing soil toxicity to algae. The method can be used in conjunction with flow cytometric analysis and facilitates the assessment of previously proposed toxicity endpoints, such as the growth zone, biomass, and photosynthetic activity. We assessed the applicability of this paper-disc soil method using the green algae Chlamydomonas reinhardtii and Pseudokirchneriella subcapitata exposed to nickel-contaminated soil; examined cell sizes, cell granularity, enzyme activity, and oxidative stress as new toxicity endpoints using flow cytometry; and identified morphological changes in green algae assayed. The results showed that, used in conjunction with flow cytometry, the extended paper-disc soil method is sufficiently sensitive to detect decreases in cell granularity in C. reinhardtii and esterase activity in P. subcapitata. The method also revealed decreases in growth zone, biomass, and electron transfer from the reaction center to the quinone pool. Collectively, the results of this study indicate that soil algal bioassays using nonspecific algae can be used to assess soil quality, to derive several toxicity endpoints for individual cells, and to evaluate previously established flow cytometric toxicity endpoints.

Rapid in situ assessment for predicting soil quality using an algae-soaked disc seeding assay

The soil quality of remediated land is altered and this land consequently exerts unexpected biological effects on terrestrial organisms. Therefore, field evaluation of such land should be conducted using biological indicators. Algae are a promising new biological indicator since they are a food source for organisms in higher soil trophic levels and easily sampled from the soil. Field evaluation of soil characteristics is preferred to be testing in laboratory conditions because many biological effects cannot be duplicated during laboratory evaluations. Herein, we describe a convenient and rapid algae-soaked disc seeding assay for assessing soil quality in the field based on soil algae. The collection of algae is easy and rapid and the method predicts the short-term quality of contaminated, remediated, and amended farm and paddy soils. The algae-soaked disc seeding assay is yet to be extensively evaluated, and the method cannot be applied to loamy sand soil in in situ evaluations. The algae-soaked disc seeding assay is recommended for prediction of soil quality in in situ evaluations because it reflects all variations in the environment. The algae-soaked disc seeding assay will help to develop management strategies for in situ evaluation.

Paper-disc method: An efficient assay for evaluating metal toxicity to soil algae

The probabilistic ecological risk assessment using terrestrial toxicity data has been mainly based on microfauna or mesofauna. Soil algae, which are food source for microfauna and mesofauna, may be alternatively used for assessing soil toxicity. However, there are no internationally recommended guidelines for soil algal bioassays, and the collection of algae from the test soils has some limitations. In this study, we suggested the paper-disc method as an easy-to-use alternative. This method has been widely used for testing the antibacterial toxicity of various chemicals in agar media by measuring the diameter of the inhibition zone around the disc. We adapted the paper-disc method for screening the toxicity of copper (Cu) and nickel (Ni) to the soil alga Chlorococcum infusionum using various evaluation endpoints, such as growth zone, chlorophyll fluorescence, and photosynthetic activity. Chlorophyll fluorescence and photosynthetic activity decreased with the increasing concentrations of Cu(+2) or Ni(+2) contaminated soils. Algal growth zone was analyzed visually and showed similar results to those of chlorophyll fluorescence. The direct ethanol extraction method and indirect culture medium extraction method were similarly effective; however, the former was easier to perform, while the latter might facilitate the analysis of additional endpoints in future studies. Overall, the results suggested that the paper-disc method was not only a user-friendly assay for screening soil toxicity, but also effective due to its association with indirect soil quality indicators.

Effects of carbaryl and 1-naphthol on soil population of cyanobacteria and microalgae and select cultures of diazotrophic cyanobacteria

Carbaryl application to soil collected from a rice fallow field was relatively less toxic to viable estimates of cyanobacteria and microalgae under nonflooded conditions than under flooded conditions. Application of 1-naphthol, the hydrolysis product of carbaryl, to soil under both the regimes increased the population of both cyanobacteria and microalgae. Soil application of carbaryl and 1-naphthol in combination, up to 1.0 kg ha(-1), was nontoxic to the viable population. The toxicity exerted by carbaryl and 1-naphthol towards growth, measured in terms of chlorophyll a, and nitrogenase activity was more pronounced in Anabaena spp. than in Nostoc spp.

Screening of PAHs and DDTs in sand and acrisols soil by a rapid solid-phase microalgal bioassay

Previously we have demonstrated the rapid screening potential of a newly developed solid-phase microalgal bioassay with spiked sands. In this paper, we report further comparative results using both PAHs and DDTs spiked sands and field-collected acrisols soils. Toxicity responses obtained from standard higher plant tests with three species of plants (Lolium perenne, Cynodon dactylon and Brassica chinensis) were compared with those obtained from a cocktail of microalgae (Selenastrum capricornutum, Chlorococcum hypnosporum and the indigenous Chlorococcum meneghini). The 5-day seed germination/root elongation tests were not sensitive at all in contrast to the 4-day solid-phase microalgal tests and the 28-day early seedling growth tests in both spiked sands and contaminated soils. Sensitivities of microalgal tests were generally higher than the seedling growth tests in spiked sands. Concerning the assays with contaminated soil, the responses of microalgae and higher plants varied. However, the results demonstrated that microalgae could generally act as effective surrogates to screen xenobiotic compounds at toxic level to higher plants, with the local species C. meneghini especially sensitive to reveal phytotoxic effects. This promising rapid screening solution is possible to be used in accompany with standard seedling growth tests when assessing phytotoxicities of contaminated areas, especially for acrisols soil.

Impact of four pesticides on the growth and metabolic activities of two photosynthetic algae

The acute toxicity was determined for soil algae Chlorella kesslerei and Anabaena inaequalis, exposed to pesticides lindane, pentachlorophenol (PCP), isoproturon (IPU), and methyl parathion (MP). Toxicity markers included growth inhibition, chlorophyll biosynthesis, and total carbohydrate content, as a function of dose and time. Concentration response functions (EC50) were estimated by probit data transformation and weighted linear regression analyses. Lindane's toxicity to Chlorella increased sharply with time (EC50 = 7490, 10.3, 0.09 mg L(-1); 24, 48, 72 h), but remained nearly constant through 72 h with Anabaena (8.7-6.7 mg L(-1); 24-72 h). PCP at low concentrations stimulated algal growth and chlorophyll a production, an effect reversed at higher doses. Anabaena was less tolerant of PCP and MP than was Chlorella. The 96-h static EC50 values for Chlorella were: 0.003, 34, 0.05, and 291 mg L(-1) for lindane, PCP, isoproturon, and MP, respectively; for Anabaena, these were 4.2, 0.13, 0.21, and 19 mg L(-1). Carbohydrate production responses were similar to those of cell density (growth) and chlorophyll biosynthesis, with MP having the lowest adverse impact. The overall relative toxicity among the four tested pesticides was: for Chlorella, lindane > IPU >> PCP >> MP; and for Anabaena, PCP > IPU > lindane > MP. The results confirm that toxicants such as these pesticides may affect individual (though related) species to significantly different degrees.

Interaction of Endosulfan and malathion with blue-green algae Anabaena and Aulosira fertilissima

The growth of Anabaena and Aulosira fertilissima was adversely affected by endosulfan even at 1 microg ml(-1). The inhibition was significantly above 50% at 20 microg ml(-1) throughout the incubation. Anabaena survived up to 500 microg ml(-1) of malathion, but was completely bleached in the presence of 50 microg ml(-1) of endosulfan. Aulosira was more sensitive to malathion than Anabaena and recovered to control levels only at 10 microg ml(-1). The morphology and hetercyst frequency were not altered in Anabaena. Aulosira cultures were dull brown in colour at 20 microg ml(-1) of endosulfan with the filaments clumping, instead of the usual mat formation. Both malathion and endosulfan considerably lowered (14)C uptake and nitrogenase activities in Aulosira. Nitrogen fixation was unaffected in Anabaena as the amounts of ethylene produced were equal to, or above, control levels. The impact of these insecticides on photosynthesis in Anabaena was only slight.