Plant uptake potential and soil persistence of volatile methylsiloxanes in sewage sludge amended soils.

Volatile methylsiloxanes (VMSs) are organosilicon compounds, ubiquitous in modern life. Due to their high use in consumer products, large amounts of these compounds are released into sewer systems, reaching wastewater treatment plants (WWTPs). Its frequent detection in sewage sludge can be of concern when considering its land application, not only due to potential negative impacts on the environment, but also on human health. In this work, the effects of sewage sludge application on plant development and crop productivity were studied, as well as VMSs persistence in the soil and their plant uptake. This study focused on 7 VMSs (D3, D4, D5, D6, L3, L4 and L5) and consisted of a 12-week greenhouse pot experiment, where sewage sludge-amended soils were used to cultivate Pisum sativum (peas). Sewage sludge application to soils had no negative effects on plant development and was tied to crop productivity improvements. Most of the VMSs were still present in soils at the end of the experiment and plant uptake and translocation of the 4 cyclic VMSs (D3, D4, D5, D6) occurred. VMSs were detected in plant tissues up to 161 ± 27 ng g-1 dw (samples of stems, leaves and tendrils), but did not exceed 50 ± 19 ng g-1 dw in peas, which did not translate into a human exposure risk due to ingestion, according to an intake risk assessment. However, soil risk assessments showed that for L5 the hazardous ratios were higher than the threshold value of 1. This means a potential environmental risk despite the low levels of this compound in soils (up to 7.3 ± 0.7 ng g-1 dw). Considering these results, sewage sludge monitoring plans should be defined for VMSs, namely when its final destination is land application, thus allowing a safer management of this residue, taking advantage of its valorization potential.

Uptake and translocation of synthetic musk fragrances by pea plant grown in sewage sludge-amended soils.

Sewage sludges are rich in organic matter and several essential nutrients for plant growth, making them very appealing for application in agricultural soils. However, they may also contain a wide range of emerging pollutants, which has raised concerns about the potential risks of this practice to crops, the environment, and public health - accumulation in soils and/or plant uptake and translocation of contaminants. Therefore, there is a need to study plant-soil interactions and assess the uptake potential of these contaminants by food crops to better understand these risks. The main aim of this work was to assess the possible drawbacks of sludge application to cropland, by observing the impact on the growth and yield of a model crop (pea plant - Pisum sativum) grown over an 86-day greenhouse experiment and by assessing the uptake potential of synthetic musk fragrances. Different sewage sludge application rates (4-30-ton ha-1) and initial concentrations of contaminants were tested. The application of sludge yielded benefits to the cultivated plants, finding improved crop productivity with an application rate of 30-ton ha-1. At the end of the experiment, soil samples and plants separated into sections were analysed using a QuEChERS extraction methodology followed by gas chromatography-mass spectrometry (GC-MS) quantification. Galaxolide (HHCB) and tonalide (AHTN) underwent uptake by the plant roots, having been detected in concentrations up to 346 ng g-1 on a dry weight basis (dw), but only HHCB was detected in above ground tissues. At the end, a decrease in the levels of synthetic musks in the amended soils (>80% in several instances) was observed. Assuming the worst-case scenario, no risk to human health was observed from the ingestion of peas grown on sewage sludge-amended soils. However, a soil hazard quotient analysis yielded worryingly high quotient values for AHTN in nearly all tested conditions.

Impacts of Microcystins on Morphological and Physiological Parameters of Agricultural Plants: A Review.

Cyanobacteria are a group of photosynthetic prokaryotes that pose a great concern in the aquatic environments related to contamination and poisoning of wild life and humans. Some species of cyanobacteria produce potent toxins such as microcystins (MCs), which are extremely aggressive to several organisms, including animals and humans. In order to protect human health and prevent human exposure to this type of organisms and toxins, regulatory limits for MCs in drinking water have been established in most countries. In this regard, the World Health Organization (WHO) proposed 1 µg MCs/L as the highest acceptable concentration in drinking water. However, regulatory limits were not defined in waters used in other applications/activities, constituting a potential threat to the environment and to human health. Indeed, water contaminated with MCs or other cyanotoxins is recurrently used in agriculture and for crop and food production. Several deleterious effects of MCs including a decrease in growth, tissue necrosis, inhibition of photosynthesis and metabolic changes have been reported in plants leading to the impairment of crop productivity and economic loss. Studies have also revealed significant accumulation of MCs in edible tissues and plant organs, which raise concerns related to food safety. This work aims to systematize and analyze the information generated by previous scientific studies, namely on the phytotoxicity and the impact of MCs especially on growth, photosynthesis and productivity of agricultural plants. Morphological and physiological parameters of agronomic interest are overviewed in detail in this work, with the aim to evaluate the putative impact of MCs under field conditions. Finally, concentration-dependent effects are highlighted, as these can assist in future guidelines for irrigation waters and establish regulatory limits for MCs.