Phosphate fertilizers represent a major source of trace metal contaminants in agricultural soils. To predict the inputs and the fate of trace metals in soils of the eastern Mediterranean region, a speciation study was conducted using a total of 44 phosphate fertilizers commercialized in the area. The contents in major anions and potentially toxic metals (Zn, Pb, Cd, and Cu) were determined using atomic absorption spectrometry (AAS) and X‐ray fluorescence spectrometry (XRF). The nature of mineral phases in the fertilizer was characterized using X‐ray diffraction and Fourier transform infrared spectrometry. The results show that sulfates are the main Cd‐bearing phases when present in the P‐fertilizer. The contents in Zn and Pb were linearly related, whereas the levels of Sb, Ag, Pd, Nb, Mo, and P2O5 were strongly correlated to each other. The annual average inputs of Zn, Cu, Pb, and Cd were calculated to be 922, 124, 26, and 6 g/ha per year, respectively. Even though such inputs comply with the maximal metals concentrations authorized in temperate countries, an accumulation of those metals in the typical arid and alkaline soils of the eastern Mediterranean countries is expected.

Soil compaction is known to drastically modify soil properties and hence to affect both plants growth and metals distribution in the soil. Phosphate amendment is generally used to improve plants production but unfortunately it also gives rise to higher metal contamination in soils and plants. In this study, the effects of various parameters on the growth of Lactuca sativa including soil density, phosphate fertilization and cadmium contamination, were investigated. In particular, the migration of cadmium in the soil columns, its accumulation and translocation in lettuces were also examined. Lactuca sativa was selected as a model plant because it is widely cultivated in alkaline clay soils of eastern Mediterranean countries. Two levels of soil compaction (1.2 and 1.4 g.cm-3), two rates of P amendment (0 and 109 mg P.kg-1), and two levels of Cd contamination (0 and 84 mg Cd.kg-1) were used in 24 model columns with a factorial randomized block experimental design. Soil compaction increased considerably both leaf area and dry weight of roots and shoots, whereas both chlorophyll content and NRA decreased. For the two soil bulk densities, the phosphate fertilizer improved lettuce growth characterized by plant height, dry matter, leaf number and NRA, whereas Cd contamination altered those parameters and increased the chlorophyll content. In soils contaminated with cadmium, the combination of compaction and phosphate fertilization resulted in a significant decrease in Cd migration along the soil columns. Cd uptake by plants increased in Cd treated soils; its accumulation was found to be more important than in plants grown in P-Cd treated soil where Cd uptake was clearly reduced in shoots and roots.

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Phytoextraction represents an innovative approach in the management of nickel (Ni) rich soils whether natural (ultramafic) or anthropogenic (contaminated sites). However, its success depends both on the production of a high plant biomass and the ability of plants to accumulate metals. The application of nitrogen (N) fertilizer can improve the biological and chemical soil fertility and thus agricultural yields. Moreover, soil microorganisms play a key role by influencing nutrient flows, which are the main limiting factors of plant growth in degraded soils. In this work, we investigated the effects of two levels of both Ni and mineral N soil applications on the microbial activities and Ni phytoextraction efficiency by Alyssum murale growing in a pot experiment during 5 months. Plant growth, nutrients and Ni uptake, soil microbial populations and their enzymatic activities involved in the biogeochemical cycles of nitrogen, phosphorus, carbon and sulfur (urease, alkaline phosphatase, β‐glucosidase and arylsulfatase, respectively) were determined. The results showed that plant dry mass was unsurprisingly not affected when the soil Ni concentration was increased. However, it led to an increase of the amount of Ni extracted per pot. A negative effect of Ni addition was observed on both total bacteria and urease activity, without any effect on other enzymes. On the contrary, N fertilizer played a significant positive role by promoting both plant growth and Ni phytoextraction, partly as a result of the stimulation and flourishing of bacterial populations.

Invertebrates have a diverse immune system that responds differently to stressors such as pesticides and pathogens, which leads to different degrees of susceptibility. Honeybees are facing a phenomenon called colony collapse disorder which is attributed to several factors including pesticides and pathogens. We applied an in vitro approach to assess the response of immune-activated hemocytes from Apis mellifera, Drosophila melanogaster and Mamestra brassicae after exposure to imidacloprid and amitraz. Hemocytes were exposed to the pesticides in single and co-exposures using zymosan A for immune activation. We measured the effect of these exposures on cell viability, nitric oxide (NO) production from 15 to 120 min and on extracellular hydrogen peroxide (H2O2) production after 3 h to assess potential alterations in the oxidative response. Our results indicate that NO and H2O2 production is more altered in honeybee hemocytes compared to D. melanogaster and M. brassicae cell lines. There is also a differential production at different time points after pesticide exposure between these insect species as contrasting effects were evident with the oxidative responses in hemocytes. The results imply that imidacloprid and amitraz act differently on the immune response among insect orders and may render honeybee colonies more susceptible to infection and pests.

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