The Metal Oxidation State in Cu, CuO, and Cu2O Nanoparticles Plays a Key Role in Toxicity to Sea Urchin Arbacia lixula, Paracentrotus lividus, and Sphaerechinus granularis Embryos

Abstract

Copper-based nanoparticles (as Cu₂O) are a key component in marine antifouling paints and, as coatings degrade, release nanoparticles that can affect a wide range of non-target organisms. This study investigates the impact of Cu₂O nanoparticles on the early development of urchins Arbacia lixula, Paracentrotus lividus and Sphaerechinus granularis, and benchmarks their toxicity against similarly sized Cu and CuO nanoparticles and ionic copper. Concentration-dependent toxicity was noted for all forms of copper at concentrations in the 1 to 5000 µg L^-1 range. EC₅₀ values after Cu₂O exposure indicated that A. lixula (99 µg L^-1) was generally more sensitive than the other two species, with EC₅₀ values of 371 µg L^-1 and 606 µg L^-1 noted for S. granularis and P. lividus, respectively. The same trend across species was noted for both Cu and CuO, although these nanoparticles generally showed higher EC₅₀ values, indicating lower toxicity compared to Cu₂O. LC₅₀ values qualitatively parallel the corresponding EC₅₀ values, with Cu₂O consistently the most toxic, while Cu was less harmful, and CuO did not reach LC₅₀ at any concentration. Again, greatest lethality was noted in A. lixula. While copper ion release from Cu was much greater than from CuO and Cu₂O, the latter showed similar or greater toxicity to developing embryos compared to Cu. This indicates that copper ions are not the sole driver of toxicity of Cu₂O, but there may also be a contribution derived from Cu₂O redox activity within cells or at membranes that negatively impact oxidative stress defence mechanisms and metabolic pathways.

Keywords: antifouling; copper; developmental defect; embryogenesis; marine; paint; skeletogenesis.

Figure 1

Temporal change in hydrodynamic diameters (d_H) of Cu, CuO, and Cu₂O nanoparticles (10 mg L⁻¹) over 48 h in ultrapure (S‧0) and in artificial seawater (S‧38).

Figure 2

Cupric ion concentration in Cu, CuO, and Cu₂O dispersions over 96 h in (a) ultrapure water and (b) filtered seawater.

Figure 3

Scoring of embryos and plutei larvae of A. lixula, P. lividus, and S. granularis after exposure to copper in ionic or nanoparticulate form as (A) normally developed, (B) developmentally delayed, and (C) undeveloped or dead. Scale bar = 100 µm.

Figure 4

Percentage of normally developed (NP), delayed development and developmental defect, (DD) and undeveloped embryos (UND) of A. lixula after 72 h exposure to (a) CuSO₄, and nanoparticles of (b) Cu, (c) CuO, and (d) Cu₂O. Statistical significance compared to the control indicated as * p < 0.05, ** p < 0.01, *** p < 0.001, and **** p < 0.0001.

Figure 5

Percentage of normally developed (NP), delayed development and developmental defect (DD), and undeveloped embryos (UND) of P. lividus after 72 h exposure to (a) CuSO₄, and nanoparticles of (b) Cu, (c) CuO, and (d) Cu₂O. Statistical significance compared to the control indicated as * p < 0.05, ** p < 0.01, *** p < 0.001, and **** p < 0.0001.

Figure 6

Percentage of normally developed (NP), delayed development and developmental defects (DD) and undeveloped embryos (UND) of S. granularis after 96 h exposure to (a) CuSO₄, and nanoparticles of (b) Cu, (c) CuO, and (d) Cu₂O. Statistical significance compared to the control indicated as * p < 0.05, ** p < 0.01, *** p < 0.001 and **** p < 0.0001.