Uptake, Partitioning, and Growth Effects of Carbamazepine Rates on Hydroponic Lettuce (Lactuca sativa)

Date

2023-08

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Abstract

Compounds of emerging concern (CEC) have created challenges in regard to water reuse during times of drought in arid and semi-arid regions. CEC’s are currently unregulated which means that CEC’s can be found in wastewater and wastewater effluents in unknown concentrations. Some examples of CEC’s include pharmaceuticals, personal care products, detergents, and more. Some of these compounds have been shown to be endocrine disruptors while others cause harm to aquatic life. A few concerning pharmaceuticals include, acetaminophen, carbamazepine, ciproflaxin, doxycycline, fluoxetine, tramadol, as well as hormones such as estrogen and testosterone. The uses for these pharmaceuticals include antibiotics, treatment for pain management, and treatment for mental disorders. As potable water quantities become less available, reclaimed wastewater has been suggested as an alternative irrigation source. Since an unknown concentration of these CEC’s remains in the wastewater after processing, using reclaimed or reused wastewater for irrigation may expose edible crops to these CEC’s. Many studies have shown that crops can uptake CEC’s and this is cause for concern as it is currently unknown how CEC’s in edible crops will affect humans who ingest these crops. While some CEC’s break down in the environment, many are persistent and resist degradation. Of these, carbamazepine is of interest due to its environmental longevity and resistance to degradation, particularly in wastewater treatment systems. Carbamazepine is used to treat various conditions, the main uses include epilepsy, bipolar I, ADHD, and trigeminal neuralgia. It has been in use in the US since the 1960s which has resulted in a large quantity of carbamazepine in the wastewater treatment system since carbamazepine is excreted in bodily waste mostly unchanged. During the wastewater treatment process, it has been found that only 7% of carbamazepine is filtered out using traditional treatment methods. While some studies have explored the uptake of carbamazepine in different situations, few show consistent results on how carbamazepine is partitioned in plant tissues that are grown in hydroponics systems. Furthermore, the rates of application are highly variable between studies. To determine how different concentrations of carbamazepine affect plant growth and partitioning in tissues, we designed two trials to evaluate the uptake and partitioning of carbamazepine in lettuce grown in a deep water hydroponic system. The hydroponics system was spiked with varying concentrations of carbamazepine in both trials, the first having lower concentrations and the second having higher concentrations. In trial 1, carbamazepine concentrations were applied at rates of 0 µg L-1, 12.5 µg L-1, 25 µg L-1, and 50 µg L-1. Trial 1 showed that these low rates of carbamazepine had few effects on lettuce growth. Accordingly, lower concentrations of accumulated carbamazepine within lettuce tissues were found during this trial. Due to the negligible effects of carbamazepine on growth, in trial 2 carbamazepine concentrations were increased to concentrations of 0 mg L-1, 21 mg L-1, 41 mg L-1, and 83 mg L-1. In trial 2, greater amounts of carbamazepine accumulated in plant tissues compared to trial 1. Additionally, lettuce treated with carbamazepine were negatively affected at rates of 41 mg L-1, and 83 mg L-1 carbamazepine. Lettuce treated with carbamazepine from trial 2 showed signs of stress and edge necrosis was noted. When considering portioning of carbamazepine, the outer leaves had the highest concentration of carbamazepine followed by the inner leaves and roots. This pattern was similar in both trials. Of the four treatments in the second trial, the 83 mg L-1 treatment had the highest concentration of carbamazepine. The primary factors that affected accumulation and partitioning of carbamazepine in plant tissues were relative humidity, solar radiation, and PPFD (photosynthetic photon flux density). In conclusion, lettuce treated with carbamazepine had variable effects on growth and accumulation were found. This correlates with applied concentrations of carbamazepine and environmental factors that affect transpiration, which affects carbamazepine uptake. Further research must be done to determine the impacts of CEC’s on plant growth and production as well as the various environmental conditions that affect CEC uptake.


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Keywords

uptake, partitioning, growth effects, carbamazepine, hydroponics, pharmaceutical, compounds of emerging concern

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