Factors affecting catalysis of copper corrosion products in NDMA formation from DMA in simulated premise plumbing

• Increasing alkalinity and hardness increased copper-catalyzed NDMA formation.
• Natural organic matter (NOM) inhibited copper catalysis of NDMA formation.
• pH influenced the speciation of chloramine and the interactions of copper with DMA.
• Copper–DMA complexation was involved in elevating NDMA formation at pH 7.
• Dichloramine formation was involved in copper-catalyzed NDMA formation at pH 7.

This study investigated the effects of corrosion products of copper, a metal commonly employed in household plumbing systems, on N-nitrosodimethylamine (NDMA) formation from a known NDMA precursor, dimethylamine (DMA). Copper-catalyzed NDMA formation increased with increasing copper concentrations, DMA concentrations, alkalinity and hardness, but decreased with increasing natural organic matter (NOM) concentration. pH influenced the speciation of chloramine and the interactions of copper with DMA. The transformation of monochloramine (NH2Cl) to dichloramine and complexation of copper with DMA were involved in elevating the formation of NDMA by copper at pH 7.0. The inhibiting effect of NOM on copper catalysis was attributed to the rapid consumption of NH2Cl by NOM and/or the competitive complexation of NOM with copper to limit the formation of DMA–copper complexes. Hardness ions, as represented by Ca2+, also competed with copper for binding sites on NOM, thereby weakening the inhibitory effect of NOM on NDMA formation. Common copper corrosion products also participated in these reactions but in different ways. Aqueous copper released from malachite [Cu2CO3(OH)2] was shown to promote NDMA formation while NDMA formation decreased in the presence of CuO, most likely due to the adsorption of DMA.

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