Levels of Lead, Copper, and Zinc in Cabbage (Brassica oleracea sp.) and Lettuce (Lactuca sativa sp.) Grown on Soil Amended with Sewage Sludge

Synchrotron induced X-ray fluorescence spectroscopy reveals heavy metal translocation in sludge amended soil-plant systems: assessment of ecological and health risks

The use of composted sludge from sewage treatment plants as a soil amendment is a common practice of recycling nutrients like organic carbon, nitrogen, and phosphorus. The sewage generated in larger cities of developing countries is often contaminated with various heavy metals (HMs) that ultimately end up in composted sludge. Thus, using such composted sludge is likely to pose ecological and human health risks. Hence, the knowledge of HM translocation in sludge-soil-plant systems is of vital importance. The present study was aimed at investigating the HM translocation in sludge-soil-plant system. The HM translocation was measured using synchrotron radiation-induced x-ray fluorescence spectrometry and atomic absorption spectroscopic techniques. The results indicated high HM mobility (up to 2628.5 mg kg-1) from sludge to spinach plant. The metal accumulation (mg kg-1) ranged in the order-Fe (950.55-2628.5) > Zn (20.11-172.13) > Cu (13.86-136.17) > Mn (2.13-34.67) > Cd (0.11-31.17) > Pb (1.50-30.16) > Co (0.18-9.85) As (0.02-7.80) > Cr (0.01-5.69). This observed accumulation depended on the volume of sewage being treated in the sewage treatment plant (STP) and varied in the order control < (8 MLD Bhagwanpur, STP 1) < (80 MLD Dinapur, STP2) < (140 MLD Dinapur, STP3) hence the HM load coming into STPs. The metal transfer factor, bioconcentration factor, and translocation factor values also correlated with the abundance of Fe, Cu, Pb, Cd, and Zn in spinach root and shoot compartments. The carcinogenic risk for heavy metal carcinogens like As, Cd, Cr, and Pb revealed children being more prone to cancer upon spinach consumption. Hence, it is necessary to assess the heavy metals present in the sludge prior to its application in agricultural fields.

Hazards of toxic metal(loid)s: Exploring the ecological and health risk in soil-crops systems with long-term sewage sludge application

Sewage sludge (SS) is commonly used as agricultural fertilizer worldwide. However, the toxic metal(loid)s in SS raises concerns about soil contamination and the potential risks to human health. This study, conducted since 2007 on the North China Plain, examines the impact of SS use on crops. An experiment was designed with five treatments: conventional fertilization (CK) and four levels of SS application (W1, W2, W3, and W4: 4.5, 9.0, 18.0, and 36.0 t ha-1, respectively). Soil concentrations of eight toxic metal(loid)s (Zn, Cu, Cr, Cd, Ni, Pb, As, and Hg) were analyzed to assess pollution risk using various indices. Health risks associated with maize and wheat grains were also evaluated. Additionally, the impact of long-term SS application on crop yield, soil quality, and human health within a wheat-maize rotation system was examined. SS application increased wheat and maize yields by 5.37 to 19.08 % and 6.97 to 17.94 %, respectively, across treatments W2 to W4. Despite the toxic metal(loid)s in the grains remaining within safe limits, their concentrations showed an upward trend, especially under the W4 treatment. Moreover, SS application significantly increased the soil Zn, Cu, Cr, Cd, Pb, and Hg levels (P < 0.05) without exceeding the national standards. The geo-accumulation index values revealed rising pollution levels for Zn, Cu, Cd, and Hg, which shifted from no contamination to moderate contamination and then to moderate-to-high contamination, yet the overall pollution level remained safe. Soil ecological risks increased from moderate to serious, with Hg posing the greatest risk, particularly under the W4 treatment. Long-term crop intake from the area significantly exposed children and adults to As, contributing 42.12 % and 34.62 % to hazard index (HI), respectively. The HI values for toxic metal(loid)s in these grains surpassed one in both age groups, suggesting health risks from long-term SS cultivated crops.

Biofertilizers from wastewater treatment as a potential source of mineral nutrients for growth of amaranth plants

Exploring alternative fertilizers is crucial in agriculture due to the cost and environmental impact of inorganic options. This study investigated the potential of sewage-derived biofertilizers on the growth and physiology of Amaranthus cruentus plants. Various treatments were compared, including control treatments with inorganic fertilizer and treatments with biofertilizers composed of microalgae, biosolids and reclaimed water. The following traits were investigated: photosynthetic pigments, gas exchange, growth, and leaf nutrient concentrations. The results showed that the concentrations of N, P, Cu, Fe Zn and Na nutrients, in the dry microalgae and biosolids, were quite high for the needs of the plants. The wet microalgae presented high concentration of Cu, Fe and Zn nutrients while reclaimed water contained high concentration of N, K, Ca and S. Na and Zn nutrients increased in the leaf of plants treated with dry microalgae and biosolid, respectively. At the beginning of the flowering phase, total chlorophyll and carotenoids contents were lower for plants grown with wet microalgae while for plants grown with higher doses of biosolid or reclaimed water total chlorophyll was increased, and carotenoids were not affected. Lower photosynthetic pigments under wet microalgae resulted in lower photosynthetic rates. On the other hand, amendments with dry microalgae and biosolid increased photosynthetic rates with the biosolid being the most effective. Higher applications of biosolid, wet and dry microalgae produced a considerable increase in shoot biomass of amaranth, with the dry microalgae being the most effective. Additionally, reclaimed water obtained after tertiary treatment of sewage with microalgae and biosolids applied alone showed promising effects on plant growth. Overall, these findings suggest that organic fertilizers derived from sewage treatment have the potential to enhance plant growth and contribute to sustainable agricultural practices.

Composted sewage sludge utilization in phytostabilization of heavy metals contaminated soils

In phytostabilization, heavy metal-tolerant plants (e.g.,grasses) can be used to reduce the mobility of heavy metals in soils. The most important step in phytostabilization is the selection of the suitable plant species, in which growth and development can be supported by soil amendments. Sewage sludge compost could be a suitable additive, which provides nutrients for the plant species used for phytostabilization and contributes to an alternative solution for sewage sludge utilization. The aim of the study was to examine the potential of sewage sludge compost in phytostabilization for heavy metal contaminated matrices: identify the optimal ratio of sewage sludge compost to decrease phytotoxicity of the matrices, and assessment of feasible plant species for phytostabilization based on its bioaccumulation properties. In this research, perennial ryegrass (Lolium perenne), broad-leaved sorrel sorrel (Rumex acetosa), lettuce (Lactuca sativa) and cabbage (Brassica oleracea var. capitata) were used for phytotoxicity experiments as well as for testing sewage sludge compost amended phytostabilization of polluted flotation sludge and mine tailings. Sewage sludge compost increased the pH and electric conductivity of the matrices. High salt content and low acidity, altogether with heavy metals caused harmful physiological effects on plant species grown without any compost addition. In the root development test, as in the germination test, the application of 5% sewage sludge compost proved to be optimal. The lower translocation factors of broad-leaved sorrel and perennial ryegrass showed a higher rate of heavy metal accumulation in the roots. Perennial ryegrass, cabbage, and lettuce plant species reached their maximum biomass by adding 5% of sewage sludge compost. Based on the bioaccumulation, translocation and biomass properties, application of perennial ryegrass is recommended for phytostabilization of heavy metal contaminated sites. Furthermore, composted sewage sludge also had a significant effect on the reduction of heavy metal uptake by cabbage and lettuce, which highlights their role as indicator plants in ecotoxicological measurements.

Agronomic Productivity and Organic Fertilizer Rates on Growth and Yield Performance of Cabbage (Brassica oleracea var. capitata L.) in Northwestern Ethiopia

Cabbage (Brassica oleracea var. capitata L.) is a popular leafy vegetable in Ethiopia. However, the production and productivity of the crop are often constrained by several factors, such as deprived soil fertility and poor agronomic practices. Thus, a study was conducted in two locations in the East Gojjam zone of northwestern Ethiopia during the 2021/2022 cropping season to evaluate the effect of bud numbers and farmyard manure fertilizer rates on the growth and yield components of cabbage. Three numbers of cabbage buds (1, 2, and 3) and four levels of farmyard manure (0, 2.5, 5, and 7.5 tons/ha) were laid out in a 3 × 4 factorial arrangement in a randomized complete block design with three replications. Data on yield and quality were recorded and subjected to analysis of variance. The results revealed that growth, yield, and quality components were significantly influenced by the interaction effects of bud number and farmyard manure fertilizer rate. In both locations, the highest marketable (41.8 tons/ha) and total (43.1 tons/ha) yields were attained from the combined effects of 2 buds of cabbage and 5 tons of farmyard manure. The highest medium-sized heads (31.8 tons/ha) of cabbage were also recorded from the combination of 2 buds with 5 tons of farmyard manure. Moreover, the combined effects of 2 buds and 5 tons of farmyard manure showed the highest net benefit (5,679.03 US dollars) over the other treatments at the two locations. Hence, based on the results of the study, the combination of 2 buds and 5 tons of farmyard manure fertilizer can be suggested for the economical production of cabbage in northwestern Ethiopia and similar environments.