Uptake, Metabolism, and Accumulation of Tire Wear Particle-Derived Compounds in Lettuce

Abstract

Tire wear particle (TWP)-derived compounds may be of high concern to consumers when released in the root zone of edible plants. We exposed lettuce plants to the TWP-derived compounds diphenylguanidine (DPG), hexamethoxymethylmelamine (HMMM), benzothiazole (BTZ), N-phenyl-N′-(1,3-dimethylbutyl)-p-phenylenediamine (6PPD), and its quinone transformation product (6PPD-q) at concentrations of 1 mg L–1 in hydroponic solutions over 14 days to analyze if they are taken up and metabolized by the plants. Assuming that TWP may be a long-term source of TWP-derived compounds to plants, we further investigated the effect of leaching from TWP on the concentration of leachate compounds in lettuce leaves by adding constantly leaching TWP to the hydroponic solutions. Concentrations in leaves, roots, and nutrient solution were quantified by triple quadrupole mass spectrometry, and metabolites in the leaves were identified by Orbitrap high resolution mass spectrometry. This study demonstrates that TWP-derived compounds are readily taken up by lettuce with measured maximum leaf concentrations between ∼0.75 (6PPD) and 20 μg g–1 (HMMM). Although these compounds were metabolized in the plant, we identified several transformation products, most of which proved to be more stable in the lettuce leaves than the parent compounds. Furthermore, continuous leaching from TWP led to a resupply and replenishment of the metabolized compounds in the lettuce leaves. The stability of metabolized TWP-derived compounds with largely unknown toxicities is particularly concerning and is an important new aspect for the impact assessment of TWP in the environment.

Environmental Occurrence and Toxicity of 6PPD Quinone, an Emerging Tire Rubber-Derived Chemical: A Review

“…69 In the case of TRWPs, only one study has examined 6PPD and 6PPDQ absorption in plants, specifically assessing lettuce. 54 Lettuce plants were irrigated with a hydroponic solution containing 1 mg/L TRWPs such as 6PPD and 6PPDQ for 2 weeks, finding 6PPD in lettuce leaves at 0.75 μg/g. Surprisingly, among all studied compounds only 6PPDQ continued its accumulation in lettuce leaves over 2 weeks with a concentration of up to 2.19 μg/g.…”

“…It is anticipated that TRWPs, upon entering farmland soils will release their compounds on the upper soil layers rather than moving them down to deeper soil horizons . In the case of TRWPs, only one study has examined 6PPD and 6PPDQ absorption in plants, specifically assessing lettuce . Lettuce plants were irrigated with a hydroponic solution containing 1 mg/L TRWPs such as 6PPD and 6PPDQ for 2 weeks, finding 6PPD in lettuce leaves at 0.75 μg/g.…”

Ubiquity of Amino Accelerators and Antioxidants in Road Dust from Multiple Land Types: Targeted and Nontargeted Analysis

“…DPG was of the highest priority, followed by DChA, BPPG, DPCG, PPD-CHO, PPD-COC 4 H 9 , 6PPD-Q, 6PPD, CPG, and DPA. Bioaccumulative and (eco-)­toxic potential, as well as health risks and possibility of maternal transfer, have been reported for DPG, DChA, 6PPD­(-Q), and DPA. ,,,,,,,, However, the toxicological and environmental information on the remaining priority compounds remains extremely limited, which urgently requires further investigations.…”

“…As two large suites of synthetic aniline-based additives, amino accelerators and antioxidants (AAL/Os) have been ubiquitously used in numerous industrial and consumer products including rubber, lubricants, plastics, foam, and fuel. − AALs can accelerate the vulcanization processes of polymer manufacture, , while AAOs are utilized to minimize the oxidative degradation of articles during storage and use. − Many AAL/Os, including 1,3-diphenyl­guanidine (DPG) and N -(1,3-dimethyl­butyl)- N ′-phenyl- p -phenylene­diamine (6PPD), are listed as high-production-volume chemicals in the U.S. and Europe. , The fact that these chemicals are not chemically bonded to the materials they are blended with, and several decades of their large-scale applications have resulted in AAL/O-contamination of nearly all environmental compartments (particularly those subjected to heavy anthropogenic interferences) and various ecosystems. ,− Additionally, recent studies also confirmed the build-ups of DPG, diphenyl­amine (DPA), and 6PPD in humans, as well as the former’s capacity to penetrate placentas, indicating prenatal exposure. − The widespread distribution, bioaccumulative and toxic potential of AAL/Os have made them become contaminants of emerging concern, receiving an increasing number of investigations recently. − …”

“…As two large suites of synthetic aniline-based additives, amino accelerators and antioxidants (AAL/Os) have been ubiquitously used in numerous industrial and consumer products including rubber, lubricants, plastics, foam, and fuel. 1−3 AALs can accelerate the vulcanization processes of polymer manufacture, 4,5 while AAOs are utilized to minimize the oxidative degradation of articles during storage and use. 6−10 Many AAL/Os, including 1,3-diphenylguanidine (DPG) and N- (1,3-dimethylbutyl)-N′-phenyl-p-phenylenediamine (6PPD), are listed as high-production-volume chemicals in the U.S. and Europe.…”