Pesticides are widely used for pest control on farmland for crop and livestock protection and even in residential areas for the health of humans and their pets. Carbaryl (chemical name 1-naphthalenyl methyl carbamate) is a carbamate pesticide that is a widely used broad-spectrum insecticide. Carbaryl is used in agriculture, horticulture, and residential settings on corn, soybean, cotton, fruit, nut, vegetable crops, and rice, as well as in-home yards and gardens [1]. Carbaryl is used on intensive rice farmland for the control of grasshoppers and crickets that damage grasses and other vegetation by consuming the stems and leaves. Insect feeding causes direct damage to rice plant growth and seed production, thus reducing valuable grain productivity [2]. After the rice is transplanted at around 30 days, it has green leaves, which are a feed source for grasshoppers; subsequently, the rice blooms at around 90 days, with the flower inflorescence also being attractive to grasshoppers and other insects. Thus, following rice transplantation, a carbaryl application is sprayed at around 30 or 90 days or both, depending on the presence of insects, such as grasshoppers. Some carbamate pesticides, such as carbosulfan, may be applied as well if insects, such as aphids, are present [3]. In 2014, a survey of carbaryl use in agriculture in Mae Taeng district, Chiang Mai, Thailand, was conducted by the Environmental Research and Training Center that reported carbaryl was used by farmers for pest control in the area, including as a herbicide, fertilizer, and plant hormone [4]. Water sampling from the area showed carbamate residue present at 0.01 mg L⁻¹. Soil sampling detected carbaryl at <0.02 mg L⁻¹, and plant sampling recorded carbamate residue (methomyl) during the harvesting period of the yardlong bean as high as 0.02–0.08 mg L⁻¹ and in soybean sprout as high as 0.53 mg L⁻¹ [4].

Carbaryl has a water solubility of 36 mg L⁻¹ at 20 °C [2]. It moves and is transformed in the environment. The environmental fate processes include persistence and degradation, mobility and migration potential to groundwater and surface water, and plant uptake. Its degradation in aerobic soil varies from rapid to slow, with a half-life ranging from 4 to 253 days, depending on the pH and aerated soil conditions. 1-naphthol is the major degradation of carbaryl under aerobic and anaerobic conditions in soil and water. Sorption of 1-naphthol to soil also increases with increasing organic carbon content. The degradation of 1-naphthol is expected to be less persistent in the field than carbaryl [2].

Acute (short-term) and chronic (long-term) exposure of humans to carbaryl has been observed to cause cholinesterase inhibition. The reduced levels of this enzyme in the blood cause neurological effects. These effects appear to be reversible upon discontinuation of exposure. Headache, memory loss, muscle weakness and cramps, and anorexia result from cholinesterase inhibition caused by prolonged low-level exposure to carbaryl [1]. In 2008, the WHO announced that the acceptable daily intake of carbaryl is 0–0.008 mg kg⁻¹ of body weight [5]. Ecological toxicity in terrestrial and aquatic plants and animals has been observed and reported for carbaryl [2]. In 2013, the Ministry of Agriculture and Cooperatives, Thailand, announced a standard for maximum residue limits (MRL) for carbaryl in agricultural products as <0.02–10 mg kg⁻¹ [6]. The MRL for rice is 1 mg kg⁻¹ [6]. Unfortunately, carbaryl has been found at unsafe levels in some vegetables [7]. In 2019, USDA reported that carbaryl could react with nitrile under certain conditions to produce N-nitrosocarbaryl, which has been shown to be carcinogenic and mutagenic in laboratory test systems [2].

Carbaryl degrades readily to 1-naphthol, which is several times more toxic than its precursor. Despite its lower persistence in the environment and its wide distribution, there is a need to know whether and to what extent carbaryl is present because of its potentially toxic effects [8]. When present in the environment at unusually high levels, biodegradable chemicals can be extremely persistent, which increases the risk of surface and groundwater contamination. Thus, contaminated soil at agrochemical facilities requires quick, efficient and economical cleanup. Phytoremediation is one method that can remediate pesticide residue in the soil. Plants remediate organic contaminants via three mechanisms: (1) the direct uptake of contaminants and the subsequent accumulation of nonphytotoxic metabolites into plant tissue; (2) the release of exudates and enzymes that stimulate microbial activity and biochemical transformations; and (3) the enhancement of mineralization in the rhizosphere (the root-soil interface), which is attributable to mycorrhizal fungi and the microbial consortia [3,9]. Phytoremediation has been successfully used to clean up persistent organic pesticides such as atrazine, alachlor and metolachlor [10]. The removal efficiency of several plants has been reported regarding pesticides, such as carbofuran, chlorpyrifos, carbaryl, inuron, permethrin, and triazophos [3,11,12,13]. Some species, such as Phragmites sp., can remove pesticides [14,15,16], while plants, such as Phragmites australis, have been used to remove pesticide wastewater based on a wetland system [14,17]. Among these remediating plants, some can be classified as ornamental and leguminous, such as lupine, sunflower, and morning glory. The leguminous plant, Lupinus angustifolius, is tolerant to the uptake or phytoextraction of carbaryl [9,12], while sunflower can also accelerate the degradation of carbamate pesticides in soil [3]. Although marigold (Tagetes erecta) and pot marigold (Calendula officinalis) have shown evidence of phytoremediation in heavy metals [18,19], there has been little reported on using marigold to remediate carbamate pesticide. These tropical plants, sunn hemp (Crotalaria juncea L.), sunflower (Helianthus annuus L.) and marigold (Tagetes erecta), have a short life cycle and may be suitable for on-farm crop rotation in crop fields, especially as agro- and eco-tourist attractions.

Phytoextraction is the process whereby plant tissue helps to remove pollutants by direct uptake. Testing for hyperaccumulators for application in the field is important. Several plant species may be used on-site to remove more than one contaminant [16,20,21]. Plants that have the ability to perform phytoextraction are characterized by their ability to accumulate and tolerate high concentrations of pollutants while maintaining a rapid growth rate. Thus, the present research investigated using phytoextraction of a synthetic solution treated with carbaryl pesticide. The factors examined were: toxicity (in terms of relative growth rate, plant morphology and pigment contents), bioaccumulation (in terms of bioconcentration factor, translocation factor and enrichment factor), and removal efficiency (in terms of uptake capacity for carbaryl residue under hydroponic conditions).