The specific properties of nanoparticles can induce toxic or promoting effects on plant growth. We performed a meta-analysis of 173 studies to evaluate the uptake and accumulation of metallic nanoparticles (MNPs) by crops. Studies on the main cereal/vegetable crops (wheat, tomato, bean, maize, rice and cucumber) and Ag, Zn, Ce, Fe, Cu and Ti containing MNPs were mostly found; 63% of the studies used MNPs with size <30 nm, and root application accounted for 84% of all studies. Under root exposure, metal concentrations were reduced by up to 2 orders of magnitude from root through shoot to leaf. Moreover, the uptake preference of MNPs or dissolved metals was element-specific and varied among tissues. Plants accumulated generally higher concentrations of the three essential elements (Cu, Zn and Fe) than of the non-essential ones (Ag, Ce and Ti). Also, foliar application was more efficient than root exposure. Metal concentrations in shoots increased with decreasing particle size for non-essential elements, but showed a variable increase for essential elements as size decreased. Besides, the uptake of MNPs increased with more negative zeta potential (especially for Cu and Zn). Overall, the plant essential elements (Cu, Zn and Fe) were preferred taken up as MNPs, while for non-essential elements (Ag and Ce) uptake as dissolved metals was more common. We conclude that for plant nanofertilizers, foliar application of essential elements as small MNPs might be more efficient for crop uptake than the uptake of dissolved metals. Highlights Graphical Abstract

Organic amendments application has been proposed as an efficient method for remediation of heavy metals-contaminated soils. This study evaluated the performance of the water-insoluble organic material polyvinylpolypyrrolidone on decontaminating water and soil polluted by heavy metals Cu, Cd and Zn via batch trials, soil incubation and pot experiments with oilseed rape. The adsorption process of Cu, Cd and Zn by polyvinylpolypyrrolidone included a rapid step which achieved 92%, 76% and 87% of adsorption capacities within 10 min, followed with a slow step before reaching equilibrium which varied from 4 to 24 h among the three heavy metals. The maximum adsorption capacities were 327, 330 and 186 mg g⁻¹ for Cu, Cd and Zn, respectively. With application doses of polyvinylpolypyrrolidone ranging from 10 to 60 g kg⁻¹, the DTPA-extracted Cu, Cd and Zn showed 59–96%, 27–93% and 13–83% reduction compared to no addition. Moreover, the uptake of Cu, Cd and Zn by oilseed rape were significantly inhibited with polyvinylpolypyrrolidone amendments, and the effects improved with the accrual of polyvinylpolypyrrolidone. Intriguingly, the application of polyvinylpolypyrrolidone showed insignificant influences on nutrients taken up by oilseed rape. Results of the present study indicated that polyvinylpolypyrrolidone is a promising organic amendment for heavy metal (Cu, Cd and Zn) stabilization in polluted water and soil.

To mitigate the exhausting of phosphate rock (PR) reserves and the widespread water eutrophication due partially to excessive phosphorus (P), efficient adsorbents are valuable. Calcium (Ca) and aluminum (Al) containing layered double hydroxides (CaAl-LDHs) showed high P adsorption capacity and potential as slow-release P fertilizers, which merits further investigation. Two P proportions (5% and 10%) of P-adsorbed CaAl-LDHs (P-LDHs) were prepared, and its effects on various soil P contents and oilseed rape (Brassica napus L.) growth were evaluated. The main components of 5%P-LDH were P-intercalated CaAl-LDH and brushite, while 10%P-LDH mainly consisted of brushite. The proportions of P were extracted from 10%P-LDH and increased in the order of 4.9% (deionized water) < 48.9% (Olsen method) < 63.5% (Bray method) < 67.4% (citric acid), which suggested that 10%P-LDH could be citrate-soluble P fertilizer. 10%P-LDH showed similar effects on soil available P with single superphosphate (SSP). Both 5%- and 10%P-LDHs showed comparable improvement with SSP on aboveground dry weight of oilseed in the red soil, while being inapparent in the Fluvo-aquic soil. The CaAl-LDH appeared capable of providing Ca for rape growth in the low initial P concentration red soil, which showed the highest dry weight when combined with SSP. The recycled P-LDHs, especially 10%P-LDH, could supply P in a comparable manner with SSP for oilseed rape P uptake. Based on trials conducted under controlled conditions, our study suggested a promising production route of commercial P fertilizer alternatives via water P removal by CaAl-LDH. Further validations with realistic wastewater P removal by CaAl-LDH and via field scale growth trials are still needed before wide application of the alternative P fertilizer production procedure reported in the present study.