Abstract
The compliance of crab shells traditionally used as a complex natural product for agricultural soil amendment with modern biofertilizers’ quality and safety requirements was investigated. Shells waste from the Blue crab, Callinectes sapidus and the Green crab, Carcinus aestuarii were tested for macronutrients, heavy metals, bacteria content, and antimicrobial properties. Such information is crucial for further utilization of the biogenic powders for any composite formulation in added-value by-products. The calcium carbonate-rich hard tissue yield was 52.13% ± 0.015 (mean ± S.D.) and 64.71% ± 0.144 from the blue and green crabs, respectively. The contents of Pb, Ni, Zn, Cr (VI), and Cu were several orders of magnitude below the prescribed limit by EU biofertilizer legislation, with Fe, Mn (not prescribed), and As being the most abundant. The content of As and Cd from the material considered here was within limits. The shells contain no colony-forming units of Salmonella spp. and compliant levels of Escherichia coli; moreover, the shell micro-powder showed dose-dependent growth inhibition of Pseudomonas aeruginosa and Staphylococcus aureus. In summary, the waste crab shells present a complex natural product as plant biofertilizer following the circular economy concepts.
Highlights
Crab shells are a known source of chitin [1]; the utilization of the shell biocomposite as a whole has only recently been a subject of deeper technological investigations [3,4,5,6]
The size of powder particles is lowered below 100 μm after only 5 min of milling, as determined by dynamic light scattering (DLS; Figure S1)
Our study indicates that the exceeding crab shell content of As and Cd, reported here at 22.5 to 46.1 and 3.78 to 5.07 mg kg−1, is a critical parameter for further processing and indicates that heavy metals analysis should be conducted on shell material when industrial pollution is suspected
Summary
In an era driven by global environmental changes, sustainable agricultural practices using molecular and complex natural products have the potential to become key alternatives towards the transition to a green circular economy [1,2]. It has been known that marine organisms, especially the crustacean shells, are a reservoir of still insufficiently exploited or resources [1,2]. Crab shells are a known source of chitin [1]; the utilization of the shell biocomposite as a whole has only recently been a subject of deeper technological investigations [3,4,5,6]. The safe and sustainable use of crabs in agrotechnology requires a knowledge-based approach and insights into which chemical or microbiological parameters are critical to avoid potential environmental pollution or crop under-performance
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