Crosslinked polyethylene (PEX) drinking water pipe: Carbon leaching, impacts on microbial growth, and developmental toxicity to zebrafish

•PEX pipe leaching and contact water toxicity was directly evaluated.•Plastic pipe carbon leaching increased with elevated water temperature.•Chemicals leached caused microbial growth to increase compared to glass controls.•Developing zebrafish exposed to PEX waters exhibited body and brain length changes.•Animal studies are recommended to understand human health effects of PEX water. Crosslinked polyethylene (PEX) is commonly used for building plumbing pipes, water supply connectors, dip tubes, and sometimes as buried water service lines. During periods of plumbing stagnation, drinking water chemistry and microbiology changes may occur, especially during building startup when the plumbing is new. The study objectives were to (1) characterize drinking water total organic carbon (TOC) concentration changes caused by PEX and cell growth; (2) identify compounds leached using two extraction approaches; and (3) directly measure acute and developmental toxicity effects of the PEX contact waters. A series of short- and long-term stagnation experiments were conducted. Of the three different PEX pipe brands examined, the PEX-b brand exhibited the highest organic carbon migration (24 to 120 hours range: 7.24 to 15.4 mg/L). Total cell counts increased for all three PEX types and conditions over the 120 hour exposure period at 55°C. The simulated 60-day exposure period revealed TOC levels were greater at 55°C, compared to 23°C. When zebrafish were exposed to PEX contact waters, morphological alterations (changes in zebrafish body and brain length) were observed, but no impact on survival or behavior patterns was detected. Exposure to PEX-b and PEX-c brand waters at 23°C caused a decrease in animal total body length and brain length compared to larvae in the control group. A increase in the ratio of head length to body length was observed for animals exposed to the room temperature PEX-a group, which indicates abnormal development compared to the control group. Additional studies are recommended to characterize the type and magnitude of contaminants leached and directly measure the toxicity of the resulting waters.