Environmental Impact of Biodegradable Packaging Based on Chia Mucilage in Real Water Bodies

Abstract

The intense demand for alternatives to conventional plastics has increasingly motivated the development of biodegradable packaging. However, the ecological impact of these materials when discarded in natural settings has not yet been evaluated. Therefore, this study investigated the effects of films based on chia mucilage in different aquatic environments. The solubilization time varied according to water type, ranging from 40 min in ultrapure, deionized, and distilled water to 230 min in saline water. After solubilization, all water samples exhibited increased turbidity (from 1.04 to 15.73 NTU in deionized water) and apparent color (from 0 to 44 PCU in deionized water) as well as pH variations depending on ionic strength. Deionized water also showed the highest viscosity increase (>350 Pa·s at 1 s⁻¹). UV–Vis spectra revealed a moderate rise in absorbance between 236 and 260 nm, indicating organic compound release. Regarding phytotoxicity, the solubilized films had no toxic effect and promoted a biostimulating effect on root elongation, with Relative Germination Index values exceeding 140% in most samples. These results reinforce the potential of chia-based films for controlled disposal, particularly in low-salinity environments, while highlighting the importance of evaluating post-solubilization interactions with aquatic systems.

1. Introduction

Plastic packaging plays a significant role today in modern society, as it is widely used to store, protect, and extend the shelf life of various products, especially food. Although they are highly resistant, versatile, and have a low production cost, plastics are associated with improper disposal and high durability (more than 400 years), making them a significant environmental problem, with an increasing presence in aquatic ecosystems [1]. In Brazil alone, approximately 7.04 million tons of plastic were produced in 2023, of which only 25.6% were recycled or reused, highlighting both the material’s widespread use and the challenges in managing its waste [2].

At the same time, with increasing global concern for environmental conservation, the Sustainable Development Goals (SDGs) aim to mitigate the problem of plastic pollution. SDG 9 (industry, innovation, and infrastructure), SDG 12 (sustainable consumption and production), SDG 14 (life below water), and SDG 15 (life on land) are particularly relevant to efforts aimed at replacing conventional plastic with biodegradable alternatives [3]. In this context, research efforts have intensified to promote the development of more sustainable materials, focusing on biodegradable packaging that can maintain food quality and safety while reducing environmental impact [4].

Chia (Salvia hispanica L.) is a plant of the Lamiaceae family, which produces seeds that, when hydrated, release a transparent and viscous substance called mucilage. This mucilage represents 6% of the seed and is composed mainly of soluble fibers, including approximately 85% monosaccharides, 8% proteins, and 1% oil [5,6]. Chia mucilage has gained increasing attention as a promising biopolymer for the development of biodegradable films due to its excellent technofunctional properties [7,8,9,10,11], including its high biodegradation capacity under environmental conditions.

Although numerous studies have evaluated the degradation of biodegradable films, most are limited to determining the degradation and biodegradation time under soil, composting, or accelerated tests, neglecting the possible effects caused after solubilization in aquatic and terrestrial environments [12]. The biodegradability of films does not guarantee their environmental safety, since once discarded in nature, they may interact with different water types and alter their physicochemical characteristics. In addition, the rapid solubilization of films, such as those based on mucilages, can release colloidal particles, organic compounds, or ions, with potential implications for water stability and aquatic organisms [13].

There is an evident gap in the literature regarding the impact caused in aquatic environments after the solubilization of biodegradable films, which makes it extremely relevant to evaluate the behavior of the films in different types of water with distinct characteristics. Therefore, this study aimed to evaluate the impact of the solubilization of biodegradable films based on chia mucilage in real and controlled aquatic scenarios through the analysis of physical-chemical parameters before and after solubilization, as well as their phytotoxicological impact.

2. Materials and Methods

Figure 1 presents a graphic illustration of this study’s strategy. The process includes chia mucilage extraction, homogenization with pH adjustment and plasticizer incorporation, heat treatment, and drying, followed by solubilization in different types of water and evaluation of physicochemical and phytotoxicological parameters.

2.1. Water Collection

Saline water was collected from Cassino Beach (−32.1630422° S, −52.0985726° W), brackish water from Lagoa dos Patos (−32.0291558° S, −52.2457843° W), and freshwater from a spring located in the rural area (−32.0284681° S, −52.2484506° W) of Rio Grande, Brazil. The collection of water from real scenarios was collected according to ABNT NBR 9898:1987 [14] and classified according to salinity and CONAMA Resolution No. 357/2005 [15]. Distilled, deionized, and ultrapure water were obtained under controlled laboratory conditions.

2.2. Development of Biodegradable Film

The films were produced using the casting technique described by Fernandes et al. [7], employing a 1% solution of oven-dried chia mucilage [5]. The solution was homogenized for 40 min, followed by pH adjustment to 9. Glycerol was then added in a ratio of 1:3 (chia mucilage/glycerol). The film-forming solution was heated to 80 °C using a thermostatic bath (Brookfield, TC-102, New York, NY, USA) and homogenized for 30 min (Fisatom, 712, São Paulo, Brazil). The film-forming solution was then poured into 9 cm diameter Petri dishes and dried at 40 °C for 12 h in a forced-air circulation oven (Quimis, 314D, São Paulo, Brazil).

2.3. Solubilization Test

The solubilization of the films was evaluated in six types of water (saline, brackish, fresh, distilled, deionized, and ultrapure) following the method proposed by Gontard et al. [16] with modifications. The films were cut into 1 cm² squares and immersed in 50 mL of water at room temperature under constant agitation (175 rpm) using a shaking incubator (Cientec, model CT-712RNT, Viçosa, Brazil) to simulate aquatic environment dynamics.

2.4. Time for Solubilization

The total solubilization time of the films was recorded, defined as the interval required for complete visual disintegration, with no visible solid fragments remaining in the medium. Observations were conducted at regular intervals (every 10 min) until the film structure was entirely absent.

2.5. pH

The pH of the water was determined before and after solubilization using a benchtop pH meter (Quimis, Q400AS, São Paulo, Brazil).

2.6. Salinity

The electrical conductivity (σ, mS/cm) was measured using a digital conductometer (Hanna, EC 2015, São Paulo, Brazil) and salinity was calculated based on the conductivity values using Equation (1).

$$\mathrm{Salinity} (\%) = \left({\sigma }^{1.0878}\right)\left(0.4665\right)$$

(1)

2.7. Turbidity

Water turbidity was obtained using a portable turbidimeter (Akso, AK410, São Leopoldo, Brazil).

2.8. Apparent Color

The color of the water was evaluated using a photometer (Hanna, HI83399-02, São Paulo, Romania).

2.9. Total Hardness

The determination of the total hardness of the water was performed by complexometric titration with EDTA. A 20 mL aliquot of the sample was transferred to a 250 mL Erlenmeyer flask, followed by the addition of 2 mL of a pH 10 buffer solution to ensure optimal conditions for metal ion complexation. After this, a small amount of 1% Eriochrome-T black indicator was added, responsible for forming a reddish complex with the calcium and magnesium ions. The sample was then titrated with a 0.01 mol/L EDTA solution, added dropwise until the solution turned pure blue, indicating the end point. The volume of EDTA consumed was recorded, being directly proportional to the total concentration of calcium (Ca²⁺) and magnesium (Mg²⁺) ions present in the sample.

2.10. Viscosity

Viscosity analysis was performed using a rheometer (Brookfield, RVDV-III Ultra, Brookfield, WI, USA) on samples before and after solubilization of the chia mucilage film.

2.11. Ultraviolet and Visible (UV–Vis) Spectra

Absorption UV–Vis spectra of waters were recorded using an Ultraviolet Spectrophotometer (Shimadzu, UV-2550, Kyoto, Japan) in a range of 200 to 800 nm employing quartz cuvettes with an optical path of 1 cm [17].

2.12. Germination Bioassay

Lactuca sativa (lettuce) seeds were selected for the germination bioassay due to their sensitivity to low concentrations of phytochemicals and rapid germination and growth of the aerial and root parts, in addition to their insensitivity to pH variations [18]. Seeds were surface-sterilized with 1.0% sodium hypochlorite solution for 5 min to avoid any fungal contamination, followed by three rinses with distilled water. Twenty seeds were distributed in sterilized glass Petri dishes containing filter paper (Whatman No. 1), moistened with 5 mL of either the water sample before solubilization (control) or after solubilization of the chia mucilage film [19]. Germination was conducted in an incubator (CIENLAB, CRC12CBBNA, São Paulo, Brazil) for 5 days at 25 °C.

The germination criterion was the visible protrusion of the seed coat radially, and the germination rate (GR, %) was expressed based on the seeds that germinated, according to Equation (2). The relative germination index (RGI, %) was determined to compare the treatments after the solubilized film with the control (water before solubilization of the film), according to Equation (3).

$$\mathrm{GR} \left(\%\right)= {\displaystyle \frac{\mathit{number} \mathit{of} \mathit{germinated} \mathit{seeds}}{\mathit{total} \mathit{seeds}}} \times 100$$

(2)

$$\mathrm{RGI} \left(\%\right) = {\displaystyle \frac{\mathit{growth} \mathit{of} \mathit{treatment} \mathit{after} \mathit{solubilization} \mathit{of} \mathit{the} \mathit{film}}{\mathit{growth} \mathit{of} \mathit{the} \mathit{treatment} \mathit{before} \mathit{solubilization} \mathit{of} \mathit{the} \mathit{film}}} \times 100$$

(3)

2.13. Statistical Analysis

The results were treated by analysis of variance (ANOVA) and Student’s t-test and Tukey’s test, using the Statistica 5.0 software (Statsoft, Tulsa, OK, USA). Statistical analysis was performed considering a 95% confidence level (p < 0.05).

3. Results

3.1. Time for Solubilization and Physical-Chemical Parameters

The effects of the interaction of chia mucilage films and different water types were evaluated based on film degradation and changes in the physicochemical properties of the surrounding medium.

Table 1. Solubilization time, pH, and salinity of different types of water before and after the solubilization of the chia mucilage film.

Water Type	Time for Solubilization (min)	pH		Salinity (%)
		Before Solubilization	After Solubilization	Before Solubilization	After Solubilization
Saline	230.00 ± 14.14 a	7.79 ± 0.17 a,A	7.76 ± 0.04 a,A	30.10 ± 0.26 a,A	30.67 ± 0.72 a,A
Brackish	155.00 ± 10.00 b	6.74 ± 0.13 b,A	6.90 ± 0.13 b,A	1.27 ± 0.01 b,A	1.27 ± 0.03 b,A
Fresh	156.67 ± 11.55 b	6.35 ± 0.04 c,A	6.62 ± 0.18 c,A	0.05 ± 0.01 c,A	0.06 ± 0.01 c,A
Distilled	40.00 ± 0.00 c	7.05 ± 0.04 d,A	6.11 ± 0.08 d,B	nd	nd
Deionized	40.00 ± 0.00 c	6.02 ± 0.05 e,B	6.17 ± 0.03 d,A	nd	nd
Ultrapure	40.00 ± 0.00 c	5.78 ± 0.08 e,B	6.00 ± 0.04 d,A	nd	nd

nd = not detected. Average of three values with parent deviation. The same lowercase letter in the column indicates that there is no significant difference between the means within a parameter before or after solubilization according to Tukey’s test (p < 0.05). The same uppercase letter in the line indicates that there is no significant difference between the means of the same parameter in the same type of water according to Student’s t-test (p < 0.05).

presents the solubilization time, as well as pH and salinity values before and after film solubilization.

Table 2. Turbidity, apparent color, and total hardness of different types of water before and after the solubilization of the chia mucilage film.

Water Type	Turbidity (NTU)		Apparent Color (PCU)		Total Hardness (mg CaCO3/L)
	Before Solubilization	After Solubilization	Before Solubilization	After Solubilization	Before Solubilization	After Solubilization
Saline	82.23 ± 1.29 a,B	88.23 ± 1.91 a,A	430.50 ± 2.12 a,B	507.00 ± 12.73 a,A	2167.56 ± 54.31 a,B	2535.41 ± 7.41 a,A
Brackish	25.85 ± 1.30 b,B	34.70 ± 0.56 b,A	193.33 ± 7.64 b,B	274.00 ± 5.66 b,A	278.97 ± 17.28 b,A	36.13 ± 14.81 b,A
Fresh	7.86 ± 0.11 c,B	20.20 ± 0.17 c,A	21.00 ± 1.00 c,B	77.33 ± 2.08 c,A	35.80 ±1.23 c,B	43.20 ± 3.70 b,A
Distilled	1.58 ± 0.13 d,B	9.60 ± 0.42 e,A	nd	49.50 ± 4.95 d	nd	nd
Deionized	1.04 ± 0.07 d,B	15.73 ± 0.61 d,A	nd	44.00 ± 4.24 d,e	nd	nd
Ultrapure	0.22 ± 0.03 d,B	9.66 ± 0.48 e,A	nd	33.50 ± 3.54 e	nd	nd

nd = not detected. Average of three values with parent deviation. The same lowercase letter in the column indicates that there is no significant difference between the means within a parameter before or after solubilization according to Tukey’s test (p < 0.05). The same uppercase letter in the line indicates that there is no significant difference between the means of the same parameter in the same type of water according to Student’s t-test (p < 0.05).

presents the results for turbidity, apparent color, and total hardness. These parameters help assess how different aquatic conditions influence the behavior of chia mucilage films and the potential impact of discarded biodegradable packaging on water quality. Total hardness complements pH analysis, as both are closely related to the concentration of dissolved ions in the medium, especially calcium (Ca²⁺) and magnesium (Mg²⁺), which contribute to both alkalinity and the buffering capacity of the water. Thus, comparing hardness values before and after film solubilization provides an indirect assessment of ion release from the polymeric matrix, offering further insight into the effects of the films on water quality.

3.2. Viscosity

The viscosity before and after solubilization of the films is illustrated in Figure 2. This analysis was used to assess whether the dispersion and solubilization capacity of the biodegradable films under real and simulated conditions influenced the rheological behavior of the water systems.

In Figure 2a, among the real water samples, saline and brackish water after solubilization, as well as fresh water before solubilization, showed no noticeable change in viscosity across different shear rates. Similarly, in Figure 2b, distilled water after solubilization, deionized water before solubilization, and ultrapure water before and after solubilization exhibited overlapping flow curves, indicating minimal variation in viscosity. These overlaps made it difficult to distinguish the individual profiles in the graphs.

In all tested water types, viscosity decreased with increasing shear rate, indicating non-Newtonian pseudoplastic behavior (typical of fluids that flow more easily under applied force). This shear-thinning behavior is especially characteristic of polymeric solutions, such as those containing solubilized mucilages.

3.3. UV-Vis Spectroscopy

UV-Vis spectroscopy was used to investigate the light absorption characteristics, to detect possible contaminants, and to monitor chemical changes in the samples, contributing to the evaluation of water quality and film degradation processes. The readings were performed on the different water samples containing the dissolved films, as well as on their respective reference samples (controls), as shown in Figure 3. Although a scan of 200 to 800 nm was performed, peaks were only observed up to 300 nm, indicating that the released compounds were low-molecular-weight, non-aromatic substances such as sugars and organic acids. The absence of absorbance at higher wavelengths suggests that no complex or colored molecules were present, which aligns with the typical composition of chia mucilage.

3.4. Germination Bioassay

The germination rate of Lactuca sativa seeds, the average radicle length, and the relative germination index (RGI) were evaluated to verify the toxic effects of chia mucilage films solubilized in different water types. For each condition, seeds treated with the respective water type prior to film solubilization were used as controls.

Table 3. Germination data for Lactuca sativa seeds before and after solubilization.

Treatment	Solubilization	GR (%)	Radicle Length (cm)	RGI (%)
Saline	Before	0.00 ± 0.00 a	0.00 ± 0.00 a	-
	After	0.00 ± 0.00 a	0.00 ± 0.00 a
Brackish	Before	90.00 ± 7.07 a	4.24 ± 0.30 b	148.46 ± 17.20 A
	After	97.50 ± 3.54 a	6.26 ± 0.28 a
Fresh	Before	87.50 ± 17.68 a	4.39 ± 0.47 b	128.75 ± 12.00 A
	After	82.50 ± 3.54 a	5.61 ± 0.09 a
Distilled	Before	87.50 ± 3.54a	3.69 ± 0.11 b	142.37 ± 0.66 A
	After	85.00 ± 0.00 a	5.26 ± 0.18 a
Deionized	Before	92.50 ± 3.54 a	3.54 ± 0.48 b	149.93 ± 26.56 A
	After	92.50 ± 10.61 a	5.22 ± 0.21 a
Ultrapure	Before	95.00 ± 7.07 a	3.67 ± 0.15 b	142.55 ± 27.89 A
	After	85.00 ± 14.14 a	5.20 ± 0.80 a

The same lowercase letter in the column indicates that there were no significant differences between each type of water before and after solubilization according to Student’s t-test (p > 0.05). The same uppercase letter in the column indicates that there were no significant differences in the relative germination index according to Tukey’s test (p > 0.05).

presents the germination data for Lactuca sativa in the different types of water evaluated.

The results indicated that the solubilized chia mucilage films did not exhibit phytotoxic effects; instead, they potentially promoted seedling growth stimulation. This suggests the absence of phytotoxic compounds and the presence of phytonutrients or phytostimulatory components in the tested scenarios. The biostimulant effect is illustrated in Supplementary Material, which compares seed development in water samples collected after film solubilization with their respective controls (before solubilization).

4. Discussion

Films immersed in purified waters (controlled scenarios) such as distilled, deionized, and ultrapure water show shorter solubilization times, leading to complete degradation in approximately 40 min, as observed in Table 1. Although distilled, deionized, and ultrapure water exhibit minor differences in residual ion content and pH, their similar solubilization time (40 min) can be attributed to a low concentration of dissolved ions in these systems, which favors the dispersion of mucilage in the aqueous matrix, facilitating its disintegration. Despite subtle variations in pH and trace ion content, all three types of water are characterized by very low ionic strength and minimal buffering capacity. These conditions promote rapid hydration and dispersion of the mucilage’s polysaccharide chains, without the formation of cross-links or aggregation structures. Thus, the slight physicochemical differences between these water types were not sufficient to alter the solubilization kinetics, reinforcing the role of ionic strength as the predominant factor influencing mucilage film disintegration in purified systems. Deroiné et al. [20] analyzed biodegradable materials regarding their degradation in different aquatic environments and concluded that water without minerals facilitates penetration into the polymeric structure and accelerates the disintegration process compared to seawater (rich in salts).

This behavior is evidenced by the longer solubilization times observed in water systems with higher salt concentrations, especially in saline water, where the films required approximately 230 min to degrade completely. These results reinforce that high salinity and ionic strength of this medium can hinder the penetration of water into the film matrix. Thus, the ionic composition and purity of the medium are key factors influencing the degradation rate of the films. In addition to solubility, changes in the physicochemical parameters of the samples further reflect the films’ behavior in the different media. Muñoz et al. [21] found that mucilage hydration was significantly higher when the salt concentration decreased, indicating that in media with high ionic strength, mucilage solubility is reduced. This suggests that the presence of these compounds may promote interactions that affect the solubility and dispersion of mucilage, potentially leading to flocculation or spontaneous coagulation of the polysaccharides present. Regarding pH, in purified waters, more pronounced changes occurred after the solubilization of the films: pH slightly increased in deionized and ultrapure waters, while a significant decrease was observed in distilled water. This difference, which may seem contradictory at first, is related to the initial pH of each water type and its buffering capacity. The only variable introduced in these systems was the film, whose solubilization can release compounds (such as xylose, glucose, and glucuronic acid) from the mucilage during the solubilization process, which can influence pH [22]. Since these purified waters have an extremely low concentration of dissolved ions, their capacity to resist pH variations is limited. Thus, even though the same compounds were released in all cases, small initial variations become significant after solubilization. Overall, the chemical composition of the water in which the film is immersed affects the pH behavior, as the release of mucilage compounds may occur differently depending on the water type, which is relevant for real applications [23]. Furthermore, the absence of bicarbonates and carbonates in purified waters reduces their buffering capacity, making them more susceptible to pH changes. In contrast, natural environments generally exhibit alkalinity due to the presence of these ions, which contributes to greater pH stability in response to the release of compounds from the mucilage [24].

Although no targeted compositional analysis was performed, the UV–Vis spectra of the post-solubilization waters revealed absorbance in the 236–260 nm region (data shown below), consistent with the presence of organic compounds such as sugars and carboxylic acids. These findings, aligned with the known chemical profile of chia mucilage, support the hypothesis that pH variations are linked to the release of these components into the aqueous medium.

This pattern is consistent with the results observed in the saline, brackish, and freshwater samples, where pH remained statistically unchanged after the film solubilization, suggesting that the interaction with the material did not significantly alter the acidity of these media. This indicates that the released compounds, such as sugars and uronic acids from the mucilage, are not sufficient to disrupt the acid-base balance of these systems, likely due to the buffering capacity conferred by the presence of dissolved ions. This effect is particularly relevant from an environmental point of view, since the ideal pH range for most aquatic organisms is between 6.5 and 8.5, and changes outside this range can compromise the ecological balance [25]. Salinity levels remained statistically consistent across the different water types, even after film solubilization. In the controlled water scenarios, even after solubilization of the film, salinity (total concentration of dissolved salts) was not detected. This is expected given the nature of these purification processes: distilled water undergoes salt removal by evaporation, deionized water through ion exchange, and ultrapure water through a combination of advanced techniques, including pre-filtration, reverse osmosis, ion exchange resins, filtration, and exposure to UV radiation. In contrast, a statistically significant increase in turbidity (presence of suspended solids) was observed in all water types after film solubilization. This occurrence can be attributed to the release of suspended particles resulting from the degradation of the mucilage film. In addition, it is important to consider that turbidity in purified waters may have been influenced by external factors, such as vial or equipment contamination, handling errors, or inefficiencies in the purification systems, such as saturated resins and biofilm formation (slime). Despite these possibilities, the tendency for increased turbidity is consistent with the dispersion of film particles in media with lower ionic strength. In the real water—saline, brackish, and fresh—chia mucilage films exhibited the formation of aggregates with impurities present in the medium after the solubilization. These aggregates resulted in the decantation of the material to the bottom of the container when the water was allowed to settle after a while. Therefore, it can be observed that the presence of salts in the medium hinders the diffusion of water within the film, which contributes to the structural integrity of the polymer and delays its disintegration process [20]. This phenomenon may be the result of the interaction of the mucilage with organic matter and dissolved salts, forming visible and dense flakes, indicative of coagulation/flocculation mechanisms. Such processes are particularly relevant in lentic aquatic environments, those characterized by still or slow-moving water, such as lakes, ponds, dams, and reservoirs. The deposition of material at the bottom of these systems may contribute to depth reduction, alterations in benthic communities, and increased oxygen consumption due to the accumulation of organic matter.

A significant increase in apparent color was observed in all water types after film solubilization, indicating the release of dissolved solids from the chia mucilage. This behavior is expected for materials rich in water-soluble organic compounds [22]. Although elevated color values can reduce light penetration into the water column and consequently limit the euphotic zone and photosynthesis of aquatic organisms [26], the actual environmental impacts will depend on the concentration of the material applied, the flow rate in the body, and local conditions (such as temperature and pH). Therefore, although the color change is an important indicator to be monitored, the data obtained do not allow us to infer direct impacts, reinforcing the need for additional studies in systems that more closely mimic natural aquatic environments.

In the distilled, deionized, and ultrapure water samples, before and after film solubilization, total hardness was not detected, indicating that the film did not release calcium or magnesium ions in concentrations sufficient to alter this parameter. In contrast, in the real water systems, a significant increase occurred after the chia mucilage film solubilization, as can be seen in Table 2. This increase suggests the release of calcium and magnesium ions from chia mucilage. Chia mucilage presents a relevant mineral profile, with significant levels of these elements, as reported by Ikumi et al. [27]. The reported behavior partly corroborates the findings of Singh [28], who observed that, in freshwater environments, the impact of biodegradable materials on water quality was negligible, with only slight changes in the levels of dissolved oxygen, nitrates, and phosphates.

According to Figure 2a, the viscosity of saline water before and after solubilization was practically zero, indicating that there was no release of viscous compounds from the film in this medium, probably due to the inhibition of solubilization by high salinity, which can cause the collapse of the hydrophilic structure of the mucilage. In the case of brackish water, although a measurable viscosity was observed before solubilization (~120 Pa·s at 1 s⁻¹), the profile remained stable after solubilization, suggesting that the mucilage did not significantly alter the viscous behavior of the medium. Fresh water, on the other hand, showed the opposite behavior, with a slightly higher viscosity after solubilization, indicating a possible release of viscous constituents from the film (ions such as Na⁺ and Cl⁻), reflecting a more efficient solubilization in this type of water.

In Figure 2b, of the controlled scenarios, before solubilization, only the viscosity of distilled water was high. Deionized water presented the highest viscosity recorded among all waters after solubilization due to the high solubilization of chia mucilage, releasing many polysaccharides, conferring high viscous content. This sharp increase in viscosity (>350 Pa·s at 1 s⁻¹) may be attributed to the efficient release and full hydration of mucilage-derived polysaccharides in a low-ionic-strength environment, favoring molecular expansion and network formation. However, this explanation is based on the known behavior of chia mucilage in solution and not on direct analysis of the dispersed fraction. Therefore, future studies should consider applying techniques such as Dynamic Light Scattering (DLS) to evaluate particle size distribution, aggregation state, and colloidal behavior of the solubilized components to elucidate the mechanisms responsible for the observed rheological profile. The viscosity of ultrapure water was consistently low before and after solubilization, indicating that the polymers released from chia mucilage did not organize into a structured viscous network. This behavior may be associated with the total absence of ions in ultrapure water, which limits the electrostatic repulsion and chain expansion necessary for mucilage hydration and viscosity development. As reported in previous studies, certain levels of ionic strength are essential for proper polymer unfolding and intermolecular interactions that contribute to viscosity.

In general, fresh and deionized water, due to their moderate ionic content, favored greater film solubilization and a consequent increase in viscosity. However, waters with extreme ionic content, in this case, saline and ultrapure water, showed low or negligible viscosity after solubilization, indicating limited solubility or low functionality of the released polymers. Hussain et al. [29] found that moderate concentrations of salts (NaCl and KCl) reduced the viscosity of chia mucilage. Muñoz et al. [21] demonstrated that low ionic concentrations associated with favorable pH maximize hydration and expansion of the mucilage, promoting greater viscosity. These findings are consistent with the present study and help explain the collapse of the hydrophilic structure in high salinity environments (brackish and saline water) and the better solubilization in low ionic strength water (fresh and deionized water).

As shown in Figure 3c–f, the samples of fresh, distilled, deionized, and ultrapure water, respectively, with degraded film presented absorption peaks in the range between 236 nm and 260 nm, a range compatible with the absorption of parameters related to Chemical Oxygen Demand (COD), as described by Guo et al. [30], since these authors found that the light absorption caused by COD covered the spectral range from 230 to 310 nm. However, the deionized water (Figure 3e) exhibited a noticeably higher absorbance compared to the other systems, suggesting a greater release of low-molecular-weight organic compounds into the aqueous phase. This is consistent with the more efficient solubilization observed for this medium in both viscosity and visual dispersion. Furthermore, it is possible to observe that the presence of solubilized films did not cause significant changes in the spectra of these waters, other than the slight increase in organic matter in the system.

Similarly, saline and brackish water (Figure 3a and Figure 3b, respectively) presented absorption in the same range as previously mentioned; however, with a higher concentration of organic material due to the nature of the waters. However, they exhibited spectra with larger bands, possibly due to turbidity. In these cases, the characteristic COD peaks may have been masked, since suspended particles promote light scattering throughout the spectral range, resulting in deviations in the absorbance measurements [30].

The possible occurrence of spectral overlaps between nitrate and COD in the range of 230 to 250 nm is also considered, as pointed out by Guo et al. [30], which may indicate the presence of nitrates in the samples, although not directly measured in this study. Additionally, a recurring noise was observed in the range of 226 to 236 nm in all samples. including the spectra of purified waters without films (deionized, distilled, and ultrapure), which suggests that this response is not associated with the films but rather with optical or residual interference from the reading system itself.

In general, it was possible to assess that the solubilization of chia mucilage films did not cause significant changes in the absorbance spectra of the different waters evaluated, indicating low interference in the analyzed range.

As shown in Table 3, no germination was observed in the saline water treatment after film solubilization, resulting in a germination rate of 0% and, consequently, no measurable root length. However, the corresponding control also exhibited no germination, indicating that the absence of seed development was primarily due to the extreme salinity of the water, rather than any effect from the film. Across all treatments, no significant differences were observed in germination rates before and after film solubilization, indicating that the presence of the chia-based films did not exert a phytotoxic effect on the germination process.

Although there was no difference in germination rate between treatments, all treatments with film solubilization, except for saline water, showed a significant increase in radicle length. These results suggest that the components released by chia mucilage, possibly polysaccharides or phenolic compounds, had a biostimulant effect on the root growth phase. All RGI values are calculated based on radicle length prior to film solubilization exceeded 100%. According to Cuervo Lumbaque et al. [17], RGI values above 120% are indicative of stimulatory effects on root elongation.

This indicates that the seeds exposed to the dissolved films showed greater root growth, reflecting different levels of response to contact with the compounds released by the films. The RGI values did not show significant differences between the treatments, showing that regardless of the water type used, the chia mucilage film can enhance germination. Singh [28] reports that high RGI values may suggest a possible nutritional enrichment of the environment and, consequently, a risk of nutrient pollution due to excessive stimulation of plant growth and its ecological impacts, such as eutrophication. However, the results obtained in this study did not reflect such adverse effects, suggesting that the release of compounds from the films does not pose a relevant environmental risk in terms of nutrient pollution.

5. Conclusions

Chia mucilage films demonstrated promising behavior regarding their biodegradability, especially in purified water, in which they presented rapid solubilization. On the other hand, in environments with higher ionic contents (real scenario), a longer solubilization time was observed. The observed physicochemical changes, such as increased turbidity, color, and slight variations in pH, hardness, viscosity, and salinity, reinforce that compounds originating from the mucilage are released into the environment, contributing to the characterization of the degradation process. The phytotoxicity test demonstrated that the film released compounds that did not significantly alter the germination rate but stimulated early root development, resulting in longer radicles in most treatments. Therefore, although it did not improve germination percentage, the film had a beneficial bioeffect by enhancing seedling vigor, which is considered a positive indicator of environmental compatibility. These results highlight the viability of these films as sustainable alternatives for packaging if they are discarded in environments compatible with their structure. Finally, it is recommended that future research explore the modification of the film formulation to improve its performance in high-salinity environments. Strategies such as the addition of hydrophilic agents or adjustments in the pH of the matrix can broaden the spectrum of environmental applications of these biopolymers.