Potential hazards of typical small molecular organic matters in shale gas wastewater for wheat irrigation: 2-butoxyethanol and dimethylbenzylamine

Abstract

2-butoxyethanol (BE) and dimethylbenzylamine (DMBA) are small molecular organic compounds commonly found in shale gas wastewater (SGW) and environmental samples, yet their environmental risks in exposure and irrigation reuse have not been thoroughly studied. From the perspectives of physicochemical properties and toxicity, seven groups of irrigation treatment were designed for wheat irrigation according to the concentration gradient. Overall, wheat growth was normal, but higher DMBA concentrations resulted in more severe growth inhibition. The absorption of BE by various tissues of wheat was positively correlated with its concentration, while the absorption of DMBA by wheat stems showed the same trend. Interestingly, there was no significant difference in the absorption of DMBA by wheat grains in different groups. The detection results of nutritional and heavy metal elements in wheat tissues showed that the presence of organic compounds changed the relative sensitivity of wheat leaves and grains to some elements (such as Mg, Mn, Mo, etc.) enrichment. The Cd and Pb contents of wheat grains in all groups complied with national safety standards, but the As or Cr concentration in wheat grains treated with BE or DMBA exceeded the limits in some cases. Transcriptome sequencing, GO annotation, and KEGG enrichment analysis revealed similar gene functions and metabolic pathways enriched by BE and DMBA. The safe and sustainable agricultural reuse of SGW still has great potential as a promising water resources management strategy.