Mangrove biochar residue was used for nitrogen adsorption and retention in sediment, which is beneficial for plant germination. The present study investigated the effect of contact time (5–360 min), biochar dosage (0.2–2 g L⁻¹), pH (5–6), and initial concentration (2–10 mg L⁻¹) on NH₄⁺-N and NO₃⁻-N adsorption. Three different adsorption isotherm models were used to fit the experimental data. Column leaching experiments were conducted to investigate the effect of biochar with sediment from a shrimp pond on nitrogen leaching at varying biochar dosages (0–8% w/w). The results showed that the maximum percentage of both NH₄⁺-N and NO₃⁻-N adsorption was achieved at an equilibrium contact time of 240 min, with an adsorbent dosage of 2 g L⁻¹, and pH at 5.5 and 5, respectively. The adsorption of NH₄⁺-N and NO₃⁻-N were fitted to the Freundlich model and the adsorption process followed the physisorption and ion exchange. The addition of 8% biochar reduced both cumulative water volume and nitrogen leaching from the sediment. The biochar amendment increased the relative abundance of nitrifying and denitrifying bacteria in the sediment. This result suggested that biochar amended with sediment could be useful for nitrogen loss reduction.

Drinking water contamination by toxic elements poses significant public health risks, particularly in rural communities. This study quantified Pb, Cd, Zn, Cu, and K in 100 household drinking-water samples from Kratie Province, Cambodia, using atomic absorption spectrophotometry following acid digestion. Health risks for children and adults were assessed using exposure parameters obtained from a survey of 147 local participants. Zn and Cu concentrations remained within World Health Organization (WHO) guideline values, whereas Pb and Cd exceeded the applicable limits. Cd exceeded the WHO guideline value by up to 7.5-fold in 69% of samples. K showed the highest concentration among the investigated elements and was considered an indicator of dissolved-ion content. All hazard quotients were below 1 except for Cd. The cumulative hazard index exceeded 1 for children (2.46) and adults (2.07) under a conservative screening scenario, with exceedance persisting across all tested approaches for handling non-detects. The estimated lifetime cancer risk for Cd exceeded 1 × 10–4 across the published range of oral slope factors considered, although these factors were not validated for oral exposure to Cd. These preliminary risk estimates are based on a single sampling round and modelled intake assumptions. Further monitoring and investigation of potential contamination sources are recommended to better understand the extent of the problem.