Monoterpenes, the major constituents of essential oils, are known for their diverse biological activities. This study was conducted to assess the herbicidal effect of six monoterpenes viz. (R)-carvone, 1,8-cineole, cuminaldehyde, (S)-fenchone, geraniol, (S)-limonene, and (R)-linalool on barnyardgrass under laboratory and glasshouse conditions with a view to explore the possibility of their utilization for future weed management. The effect of monoterpenes on chlorophyll contents and total phenolic compounds was also evaluated. The inhibitory effects of monoterpenes on seed germination and seedling growth were tested at concentrations of 1, 2, 4, 6, and 8 mM. The results showed that geraniol and (R)-carvone caused greatest reduction of seed germination with complete inhibition at the concentrations > 2 mM. Similarly, these two compounds were the most potent inhibiters for root and shoot growth. In general, monoterpenes were less effective against seed germination than seedling growth. Furthermore, the inhibition of root growth by all compounds was greater than that of shoot growth. In foliar application treatments under glasshouse conditions, the monoterpenes reduced the fresh and dry weights, and shoot length of two-leaf stage barnyardgrass at concentrations of 1 and 2%. In addition, the tested monoterpenes caused phytotoxicity symptoms, mainly chlorosis and necrosis, followed by weed death. Complete weed control was observed in the treatments with 1 and 2% of geraniol, and 2% of cuminaldehyde. Further, a reduction of chlorophyll contents and total phenolic compounds of barnyardgrass leaves was noticed, indicating that the monoterpenes cause adverse effect on photosynthesis and weed metabolism. Based on the results of this study, it can be concluded that the monoterpenes, particularly geraniol, (R)-carvone, and cuminaldehyde, can be used as potential natural herbicides.

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The research was designated to study the ability of plants to bio-accumulate, translocate and remove the heavy metals, lead and cadmium from contaminated soil. The herbal plant ryegrass, Lolium multiflorum was investigated as a bio-accumulator plant for these metals. The translocation of these heavy metals in the herbal plant was compared considering root to shoot transport and redistribution of metals in the root and shoot system. The trace metal contents from root and shoot parts were determined using atomic absorption spectrometer. The results showed that the percent of lead and cadmium transferred to ryegrass plant were averaged as 51.39, and 74.57%, respectively, while those remained in the soil were averaged as 48.61 and 25.43% following 60 days of treatment. The soil-plant transfer index in root and shoot system of ryegrass was found to be 0.32 and 0.20 for lead, and 0.50 and 0.25 for cadmium. These findings indicated that the herbal plant ryegrass, Lolium multiflorum is a good accumulator for cadmium than lead. The soil-plant transfer factor (the conc. of heavy metal in plant to the conc. in soil) indicated that the mechanism of soil remedy using the investigated plant is phytoextraction where the amounts of heavy metals transferred by plant roots into the above ground portions were higher than that remained in the soil. The method offers green technology solution for the contamination problem since it is effective technology with minimal impact on the environment and can be easily used for soil remedy.

Environmental risk assessment of pesticides often uses the Risk Quotient (RQ) method to characterize risk quantitatively. Toxicological effects of pesticides (for 5 fungicides, 4 herbicides and 6 insecticides formulations) were assessed on the green alga Pseudokirchneriella subcapitata. For each tested pesticide, 96-h acute toxicity test was conducted and toxicity end-points and RQ values based on refinement of exposure concentrations were evaluated. Risk presumptions were presented along with the corresponding level of concern (LOC). Toxicity data indicated differential numerical ranking of pesticides within each pesticide category. For fungicides; mancozeb was found to be the most toxic and difenoconazole was the least toxic (3006 and 93 fold of toxicity; respectively). As related to herbicides, metribuzin was the most effective (1349 fold of toxicity), while cryomazine was practically non-toxic. Moreover, abamectin proved to be the extremely toxic insecticide (5511 fold of toxicity). Numerical ranking of toxicity was significantly correlated with the RQ ranking in most cases and depends on the nature of the pesticide, bioavailability and exposure concentrations. Associated risk presumptions proved that abamectin, lambda-cyhalothrin, chlorfluazuron and mancozeb pose the worst case acute risk to non-target organisms in aquatic ecosystem and consequently a regulatory action may be warranted in addition to restricted use classification (RQs=27.769; 21.568; 14.833 and 11.678; respectively exceeding LOC). Based on RQ values, risk presumption due to exposure of P. subcapitata to all tested insecticides represents the highly acute potential risk (RQ= 2.988-27.769 exceeding LOC). Fungicides are also presumed to pose a high risk on aquatic ecosystem but in a trend lower than insecticides. Among tested herbicides, only metribuzin and thiobencarb are presumed to pose a high acute risk on aquatic ecosystem (RQ=2.306 and 1.167; respectively exceeding LOC). The results support the hypothesis that numerical ranking of RQs can be used for the purpose of comparing potential ecological risks and such data may add to the pesticide existing database concerning the potential adverse effects of pesticides on aquatic ecosystem.