The effect of combined stresses, photoinhibition, and nutrient depletion on the oxidative stress of cyanobacteria was measured in laboratory experiments to develop the biomass prediction model. Phormidium ambiguum was exposed to various photosynthetically active radiation (PAR) intensities and phosphorous (P) concentrations with fixed nitrogen concentrations. The samples were subjected to stress assays by detecting the hydrogen peroxide (H₂O₂) concentration and antioxidant activities of catalase (CAT) and superoxide dismutase (SOD). H₂O₂ concentrations decreased to 30 µmol m⁻² s⁻¹ of PAR, then increased with higher PAR intensities. Regarding P concentrations, H₂O₂ concentrations (nmol L⁻¹) generally decreased with increasing P concentrations. SOD and CAT activities were proportionate to the H₂O₂ protein⁻¹. No H₂O₂ concentrations detected outside cells indicated the biological production of H₂O₂, and the accumulated H₂O₂ concentration inside cells was parameterized with H₂O₂ concentration protein⁻¹. With over 30 µmol m⁻² s⁻¹ of PAR, H₂O₂ concentration protein⁻¹ had a similar increasing trend with PAR intensity, independently of P concentration. Meanwhile, with increasing P concentration, H₂O₂ protein⁻¹ decreased in a similar pattern regardless of PAR intensity. Protein content decreased with gradually increasing H₂O₂ up to 4 nmol H₂O₂ mg⁻¹ protein, which provides a threshold to restrict the growth of cyanobacteria. With these results, an empirical formula—protein (mg L⁻¹) = − 192*Log((H₂O₂/protein)/4.1), where H₂O₂/protein (nmol mg⁻¹) = − 0.312*PAR²/(50² + PAR²)*((25/PAR)⁴ + 1)*Log(P/133,100), as a function of total phosphorus concentration, P (µg L⁻¹)—was developed to obtain the cyanobacteria biomass.

Arsenic poisoning is a public health problem worldwide. A few studies have reported the effects of arsenic exposure on adult cognitive function, but with limitations in the subject selection and exposure markers. Moreover, information regarding the association between arsenic exposure and biomarker of cognitive impairment is scarce. We examined the associations between arsenic exposure and adult cognitive impairment using the Mini-Mental State Examination (MMSE) and the serum levels of brain-derived neurotrophic factor (BDNF), a potential biomarker of cognitive health status. We designed a cross-sectional study that recruited 693 adult (18-60 years old) subjects from the areas of low- and high‑arsenic exposure in rural Bangladesh. The subjects' arsenic exposure levels (drinking water, hair, and nail arsenic concentrations) were measured by inductively coupled plasma-mass spectroscopy. The Bangla version of the MMSE was used as a cognitive assessment tool. Serum BDNF (sBDNF) levels were assessed by immunoassay. In this study, we found that average MMSE score and sBDNF level of the subjects in arsenic-endemic areas were significantly (p < 0.001 for both) lower than those of the subjects in non-endemic area. Our analyses revealed that both MMSE scores and sBDNF levels were decreased with the increasing concentrations of arsenic in drinking water, hair, and nails in a dose-dependent fashion. In regression analyses, significant associations of arsenic exposure metrics with MMSE scores and sBDNF levels were observed even after adjustment for several variables. Intriguingly, MMSE scores showed a significantly positive correlation with sBDNF levels. Our findings demonstrate that chronic exposure to arsenic dose-dependently decreases cognitive function in adults, with a concomitant reduction of sBDNF levels. A decreased BDNF level may be part of the biochemical basis of chronic arsenic exposure-related cognitive impairment.

In vegetation management, understanding the condition of submerged plants is usually based on long-term growth monitoring. Reactive oxygen species (ROS) accumulate in organelles under environmental stress and are highly likely to be indicators of a plant’s condition. However, this depends on the period of exposure to environmental stress, as environmental conditions are always changing in nature. Hydrogen peroxide (H₂O₂) is the most common ROS in organelles. The responses of submerged macrophytes, Egeria densa, to high light and iron (Fe) stressors were investigated by both laboratory experiments and natural river observation. Plants were incubated with combinations of 30–200 μmol m^–2 s^–1 of photosynthetically active radiation (PAR) intensity and 0–10 mg L^–1 Fe concentration in the media. We have measured H₂O₂, photosynthetic pigment concentrations, chlorophyll a (Chl-a), chlorophyll b (Chl-b), carotenoid (CAR), Indole-3-acetic acid (IAA) concentrations of leaf tissues, the antioxidant activity of catalase (CAT), ascorbic peroxidase (APX), peroxidase (POD), the maximal quantum yield of PSII (F_v F_m^–1), and the shoot growth rate (SGR). The H₂O₂ concentration gradually increased with Fe concentration in the media, except at very low concentrations and at an increased PAR intensity. However, with extremely high PAR or Fe concentrations, first the chlorophyll contents and then the H₂O₂ concentration prominently declined, followed by SGR, the maximal quantum yield of PSII (F_v F_m^–1), and antioxidant activities. With an increasing Fe concentration in the substrate, the CAT and APX antioxidant levels decreased, which led to an increase in H₂O₂ accumulation in the plant tissues. Moreover, increased POD activity was proportionate to H₂O₂ accumulation, suggesting the low-Fe independent nature of POD. Diurnally, H₂O₂ concentration varies following the PAR variation. However, the CAT and APX antioxidant activities were delayed, which increased the H₂O₂ concentration level in the afternoon compared with the level in morning for the same PAR intensities. Similar trends were also obtained for the natural river samples where relatively low light intensity was preferable for growth. Together with our previous findings on macrophyte stress responses, these results indicate that H₂O₂ concentration is a good indicator of environmental stressors and could be used instead of long-term growth monitoring in macrophyte management.