Metabolites are diverse substances produced or used in metabolism within organisms, not limited to amino acids. While amino acids, the building blocks of proteins, are indeed key metabolites, the category extends far beyond them. Metabolites encompass a wide range of molecules, including sugars, lipids, vitamins, and nucleotides, among others. They play critical roles in energy production, cellular signaling, and as intermediates in the synthesis or breakdown of more complex molecules. The metabolism of an organism generates a vast array of metabolites, each with specific functions and characteristics, reflecting the biochemical diversity essential for life's processes.

Excess marbling of pigment in molding refers to an unintentional, often undesirable, variation in the coloration of molded plastic parts. It happens when pigments do not fully mix with the base resin before or during the molding process, leading to streaks or swirls of colors. This effect can occur due to improper mixing of pigments, incorrect processing temperatures, or inconsistent material feed rates. While sometimes marbling is used deliberately for aesthetic effects, when unintended, it suggests a need to adjust the molding process parameters, including mixing practices, temperature settings, or the timing of pigment addition. To mitigate this issue, thorough mixing and precise control over the molding process are crucial.

Iron oxide, commonly known as rust, exists in several forms, the most common being Fe2O3 and Fe3O4. Generally, iron oxide is considered non-toxic to humans. It occurs naturally, is a common component of the earth's crust, and is regularly ingested in small amounts with water and food without adverse health effects. In industrial settings, inhalation of iron oxide dust over long periods can lead to siderosis, a benign form of lung disease, but this condition is usually not a significant health threat and often reversible. However, consumption of large quantities of iron, including iron from iron oxide, can lead to iron poisoning, which is mainly a risk for children who might ingest large amounts of iron supplements. The toxicity of iron oxide is thus more about the quantity and form of exposure rather than the compound itself being inherently harmful.