This study investigated the macro- and microelement profiles and bioactive substances (BAS) in the herbaceous species of the genus Rheum collected from two villages near Almaty, Kazakhstan, and the accumulation of heavy metals (HMs) in wild plants of Eastern Kazakhstan. Representative zonal species from the steppes and desert–steppes (Eastern Kazakhstan) were analyzed—totaling one hundred samples across 18 species from six families. According to the research, different plant species have a selective ability to accumulate heavy metals, even when growing in the same type of soil. Long-term observations reveal dominant patterns of HM (Cu, Zn, Mn, Co, Pb, Cd) occurrence in dry-steppe vegetation. It was found that Cu and Co demonstrate moderate bioadsorption with minimal accumulation, while Zn, Mn, and Pb show strong biological enrichment. Cadmium falls under elements with pronounced biological retention. Copper and cobalt are classified as moderately absorbed with limited buildup. Native plants in this region contain substantially greater amounts of lead relative to cobalt, and reflect cadmium–zinc geochemical specificity: Cd 3.85, Zn 0.15, Mn 0.10, Pb 0.09, Co 0.07, Cu 0.04, per Clark’s concentration index. Samples of collected Rheum tataricum L. in the village of Miyaly were found to have higher levels of flavonoids, phenolic compounds, and organic acids, while raw materials from the village of Bakbakty showed increased accumulation of anthracene derivatives and tannins. Flavonoids constituted the largest proportion of the studied groups of biologically active substances in both samples, confirming the high biological and pharmacological value of the plant material studied. The results obtained during the research can be successfully applied to the development of a strategy for the conservation of plant biodiversity in the studied areas and the sustainable management of plant resources.

The consumption of vegetable oils is steadily increasing, especially in Asian countries. Once used, the utilized cooking oils are either thrown into landfills or dumped there, endangering both the environment and people. One common method is to convert waste cooking oil (WCO) into biofuel; however, since WCO contains many free radicals, burning it releases large quantities of pollutants, meaning that disposal of WCO poses significant environmental risks. To stabilize the WCO (Cocos nucifera) before converting it into biofuel, this study analyzed the extraction, optimization, and use of antioxidant-rich bio-oil from Anisomeles malabarica leaves as a natural additive. Solvent screening revealed that a hexane–ethanol ratio of 4:2 was optimal for generating 76.7% bio-oil at room temperature. A maximum yield of 77% was attained by temperature and time optimization, which determined that 50 °C and 20 min were ideal. The extraction exhibits zero-order kinetics during the increasing phase, according to kinetic studies, with rate constants ranging from 0.54 to 1.44% min⁻¹ (R² = 0.950–0.997). The Peleg equilibrium model (average R² = 0.806) was used to describe the extraction profile. The regression equation ln(k) = 1799.3 × (1/T) − 10.828 (R² = 0.9748, p = 0.0002) was obtained using Arrhenius analysis. It was found that the compounds responsible for the antioxidant scavenging activity were found to be phytol, hexadecenoic acid, and tocopherol (vitamin E). The DPPH (2,2-diphenyl-1-picrylhydrazyl) test confirmed that 3% (v/v) bio-oil scavenged about 95% of free radicals, whereas the conjugated diene experiment demonstrated that over 90% of lipid oxidation in WCO was prevented. The combustion and emission properties of biofuel (WCB), which was created by transesterifying bio-oil-treated WCO, were compared to those of neat diesel and untreated WCO-derived biofuel (WC). In comparison to both WC50 and neat diesel, WCB50 demonstrated an equivalent in-cylinder pressure and heat release rate, but significantly reduced emissions of NO_x, CO, hydrocarbons, and smoke. These results show that Anisomeles malabarica bio-oil works well as a natural antioxidant addition for clean combustion and biodiesel stabilization.