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

Environmental context Nanomaterials are being extensively researched for use as agrochemicals, and some commercial formulations containing nanomaterials are already on the market. Information on environmental fate and effects of nanomaterials, however, are largely based on laboratory-synthesised materials. This study questions whether data on trophic transfer of Cu from pure, laboratory-synthesised Cu(OH)2 nanomaterials can be used to predict trophic transfer of Cu from a complex commercial fungicide formulation containing Cu(OH)2 nanomaterials. Abstract 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.