Comparing plant-insect trophic transfer of Cu from lab-synthesised nano-Cu(OH)₂ with a commercial nano-Cu(OH)₂ fungicide formulation

To examine whether studies conducted with highly purified, laboratory-synthesised nanomaterials are predictive of behaviour of commercial nanopesticide formulations, we studied the trophic transfer of Cu(OH)₂ manufactured nanomaterials (MNMs) by tobacco hornworms (Manduca sexta) feeding on surface-treated tomato leaves (Solanum lycopersicum). We compared laboratory-synthesised copper(II) hydroxide (Cu(OH)₂) nanowire with the widely used fungicide Kocide^® 3000, whose active ingredient is nano-needles of copper(II) hydroxide (nCu(OH)₂). All leaves were treated at rates in accordance with the product label (1.5 kg ha^-1 or 150 mg m^-2). As a control, we used highly soluble CuSO₄. Over the course of the study (exposure up to 7 days followed by up to 20 days of elimination), hornworms accumulated Cu from all three treatments far exceeding controls (ranging from ∼55 to 105 times greater for nCu(OH)₂ and CuSO₄ respectively). There were also significant differences in accumulation of Cu among treatments, with the greatest accumulation in the CuSO₄ treatment (up to 105 ± 18 μg Cu per g dry mass) and the least in the nCu(OH)₂ treatment (up to 55 ± 12 μg Cu per g dry mass. The difference in their toxicity and accumulation and elimination dynamics was found to be correlated with the solubility of the materials in the exposure suspensions (r² = 0.99). We also found that first-instar larvae are more susceptible to toxicity from all forms of Cu than second-instar larvae. Our results provide valuable knowledge on whether the ecotoxicity of commercial MNM products such as Kocide can be compared with laboratory-synthesised counterparts and suggests that predictions can be made based on functional assays such as measurement of solubility.