Root Elongation Index Research Articles

Ecotoxicity risk study of petroleum hydrocarbon contaminated soil

Petroleum is an important industrial raw material that enters the soil in large quantities due to its production and extraction, causing toxic effects on soil organisms. To evaluate the toxicity of petroleum-contaminated soil, the study was conducted to qualitatively and quantitatively investigate the ecotoxicity of petroleum-contaminated loessal soil with different levels of petroleum. Using earthworms and wheat as indicator organisms by microcosm toxicity test. The earthworm test showed that the body weight of earthworms decreased by more than 20% with the addition of 800-3,000 mg/kg TPHs and by more than 50% with the addition of 13000 mg/kg or more TPHs. The EC50 values at 7 and 14 d were 21,130 and 25,314.5 mg/kg, respectively. The number of sprouts, shoot length and root length of wheat were inhibited in the soil with petroleum, and the more severe the petroleum contamination, the stronger the inhibition. The seedling elongation index was better than the root elongation index. The experimental results showed that earthworms had the lowest EC50 values for body weight inhibition at 7 days and the lowest IC50 values for mean shoot length at 7 days in wheat, which can be used for toxicity prediction and early diagnosis of petroleum-contaminated soil.

Biodegradation of pesticide-contaminated wastewaters from a formulation plant employing a pilot scale biobed

In this work, a pilot biobed was built up to treat pesticide-contaminated wastewaters discharged from a formulation plant. The pre-treated wastewater was spiked with additional pesticides in order to simulate a scenario of higher contamination: glyphosate, atrazine, imidacloprid, prometryn and carbendazim were added to reach a final Total Organic Carbon (TOC) concentration of 70 mg L−1. An Intermediate Bulk Container (IBC) was filled with a biomixture of soil and foxtail millet stubble (50:50% v v−1), and 200 l of the wastewater was added to the system recycling tank. The recirculation to the IBC was established for 12 h. After that (Day 0), the recirculation was turned on during the assay only to maintain the moisture for 180 days. Biomixture and wastewater samples were taken periodically to analyse pesticides and phytotoxicity in both matrices. In addition, hydrolytic and phenoloxidase activities, total bacteria and yeast and fungi communities were determined in the biomixture.The designed pilot scale biobed allowed to treat wastewaters with high concentration of pesticides reaching a complete removal of glyphosate, AMPA, atrazine, carbendazim and prometryn at 180 days. A good degradation percentage of the recalcitrant imidacloprid was achieved (60%) and the biomixture showed enough biological activity to continue treating additional wastewater. The root elongation index from the germination test showed low toxicity on day 180 both in biomixture and wastewater.The millet stubble resulted an appropriate lignocellulosic material to be used in biobeds to treat a wide variety of pesticides. The application of the seed germination test proved to be a low cost and simple tool to determine the end point of the process.

Afforestation of Boreal Open Woodlands: Early Performance and Ecophysiology of Planted Black Spruce Seedlings

Open lichen woodlands (LWs) are degraded stands that lack the ability to regenerate naturally due to a succession of natural and/or anthropogenic disturbances. As they represent both interesting forest restoration and carbon sequestration opportunities, we tested disc scarification and planting of two sizes of containerized black spruce (Picea mariana Mill. (BSP)) seedlings for their afforestation. We compared treatment of unproductive LWs to reforestation of harvested, closed-crown black spruce-feathermoss (BSFM) stands. After one year, seedling survival and nutritional status were equivalent among stand types but despite higher root elongation index (REI), planted seedlings in LWs had lower relative growth rate, smaller total biomass and stem diameter than those in BSFM stands. Soil fertility variables, soil temperature, nor seedling water potential, helped at explaining this early growth response. Disc scarification significantly improved seedling first-year survival, biomass and foliar nutrient concentrations of P, Ca, and Mg. Smaller planting stock showed higher REI, higher shoot water potential, and higher foliar nutrient concentration of all but one of the measured nutrients (N, P, K and Mg). Hence, preliminary results suggest that planting of smaller containerized black spruce stock, combined with disc scarification, shows potential for afforestation of unproductive LWs. The impact of the lichen mat and other potential growth limiting factors on afforestation of these sites requires further investigation.

Biological indicators capable of assessing thermal treatment efficiency of hydrocarbon mixture-contaminated soil

In China, there are many special sites for recycling and washing the used drums, which release a variety of C5–C40 hydrocarbon mixture into the soil around the site. The remediation of these contaminated sites by thermal treatment is adopted ubiquitously and needs to be assessed. Here we report the feasibility of biological indicators applied to assess thermal treatment efficiency in such contaminated soil. A series of biological indicators, including seed germination index (SGI), root elongation index (REI), plant growth height, biomass, carbon dioxide evolved (CDE), soil respiration inhibition (SRI) and soil enzymatic activities, were employed to monitor or assess hydrocarbon mixture removal in thermal treated soil. The results showed that residual hydrocarbon mixture content correlated strongly negatively with SGI for sesamum (Sesamum indicum L.), plant height, and biomass for ryegrass (Lolium perenne L.) in the concentration ranges of 0–3990, 0–3170 and 0–2910mgkg−1, respectively. In contrast, REI for sesamum was positively correlated with residual hydrocarbon mixture content from 0 to 1860mgkg−1. In addition, both CDE and SRI demonstrated that 600mgkg−1 of residual hydrocarbon mixture content caused the highest amount of soil carbon dioxide emission and inhabitation of soil respiration. The results of soil enzymes indicated that 1000mgkg−1 of residual hydrocarbon mixture content was the threshold value of stimulating or inhibiting the activities of phosphatase and catalase, or completely destroying the activities of dehydrogenase, invertase, and urease. In conclusion, these biological indicators can be used as a meaningful complementation for traditional chemical content measurement in evaluating the environmental risk of the contaminated sites before and after thermal treatment.