To clarify the groundwater–soil–crop relationship with respect to arsenic (As) contamination, As concentration was measured in tubewell (TW) water, surface soil from farmyards and paddy fields, and fresh taro (Colocasia esculenta) leaves from farmyards in the farming villages of Bangladesh. The As concentration in TW water from farmyards was at least four times higher than the Bangladesh drinking water standard, and the concentration in fresh taro leaves was equal to or higher than those reported previously for leafy vegetables in Bangladesh. As concentration of surface soils in both farmyards and paddy fields was positively correlated with that of the TW water. Further, the concentration in surface soil was positively correlated with levels in fresh taro leaves in the farmyard. This study, therefore, clarified the groundwater–soil–crop relationship in farmyards and the relationship between groundwater–soil in paddy fields to assess the extent of As contamination in Bangladeshi villages. By extracting arsenic contaminated groundwater from a well, surface soil surrounding the well and crops planted in the surface soil became contaminated with arsenic.

The environmental behavior of paclobutrazol in soil and its toxicity were studied by field investigation and an outdoor pot experiment, and the residue of paclobutrazol was detected by gas chromatography–mass spectrometry. Field investigation has found that the residual paclobutrazol in the former succession crop could severely inhibit the growth of succeeding crops of potato; with migration and transformation of residual paclobutrazol in the soil, the stems of potato were thickened with residual amount of 1.23 mg kg⁻¹, the growth was slow, and the height of potato in soil with residual amount of 1.34 mg kg⁻¹ and the control was significantly different. The degradation dynamics of paclobutrazol fits with the first-order degradation kinetics, although T₁/₂ of paclobutrazol of the taro planting soil was 30.14–46.21 days and the residual paclobutrazol remained detectable even on day 120 after application. Taro leaves were sensitive to the stress of paclobutrazol pollution; the taro leaf thickness increased, the leaf area decreased, the chlorophyll content per area unit of taro leaf showed an obvious increased trend, and SOD and CAT activities and MDA and proline content increased significantly. Paclobutrazol promoted the tillering of taro, and the taro seedlings were dwarfed by 58.01, 63.27, and 75.88% at different concentrations. It indicated that taro had strong stress response ability under paclobutrazol pollution.

Taro stalks (TS) were modified by diethylenetriamine (DETA) to obtain the modified taro stalks adsorbents (recorded as MTSA). This kind of raw material is unprecedented and the method of modification is relatively simple. The physicochemical properties of MTSA were characterized by scanning electron microscope (SEM), FTIR, and zeta potential analyzer. The capacity of MTSA for adsorbing heavy metals under different influencing factors was tested by UV-visible spectrophotometer. The results indicated that the gaps between the microspheres of MTSA are more, which are conducive to adsorption. The MTSA might have increased the amino-functional groups which are beneficial for adsorption, resulting in an increase in the adsorption capacity of copper and nickel ions (35.71 and 31.06 mg/g) of about 5–7 times compared to bare taro stalks (5.27 mg/g and 6.08 mg/g). High Cu²⁺ uptake on MTSA was observed over the pH range of 5.5–7.0, while for Ni²⁺ the range was 7.0–8.5, and the optimum dosage of adsorbent were both about 0.80 g for Cu²⁺ and Ni²⁺. The adsorption kinetics of Cu²⁺ and Ni²⁺ on MTSA could be interpreted with a pseudo-second order and the equilibrium data were best described by the Langmuir isotherm model. Graphical abstract

The aim of this work was to evaluate the antimicrobial activities of leaves and epicarp of Citrus aurantifolia essential oil against Phytophthora colocasiae, the causative agent of taro leaf blight. Oils were extracted by hydrodistillation, and their chemical composition was determined by gas chromatography and gas chromatography coupled with mass spectrometry. Antimicrobial activities of oils were tested in vitro against mycelium growth and sporangium production. In situ tests were done on healthy taro leaves, and the necrosis symptoms were evaluated. Results showed that the essential oil extraction yields from leaves and epicarp were 0.61 and 0.36%, respectively. Limonene (48.96%), bornyl acetate (14.18%), geraniol (10.53%), geranial (3.93%), and myrcene (3.14%) were the main components in leaf oil, while limonene (59.09%), cis-hydrate sabinene (7.53%), geranial (5.61%), myrtenol (5.02%), and terpinen-4-ol (3.48%) were the main components in epicarp oil. Both oils exhibited antimicrobial activities with total inhibition of the mycelium growth at 500 and 900 ppm for leaf and epicarp, respectively. The highest inhibitory concentration of sporangium production was 400 (72.84%) and 800 ppm (80.65%) for leaf and epicarp oil, respectively. For the standard fungicide (metalaxyl), the total inhibition value of mycelial growth and sporangium production was 750 ppm. In situ tests showed that, at 5000 ppm, total inhibition (100%) was obtained for a preventive test, while 50% of the inhibition was observed for a curative test when leaf oil was applied. When epicarp essential oil was applied at 5000 ppm, 47.5 and 16.66% of the reduction of leaf necrosis were observed for the preventive and curative test, respectively. There were positive correlations between both the oil concentration and the reduction of necrosis caused by P. colocasiae. These findings suggest that the C. aurantifolia essential oil could serve as an eco-friendly biocontrol for the management of taro leaf blight.