1. Introduction
Plastics represent the dominant fraction of marine litter, and less than 10% of the plastics used worldwide are recycled [
1,
2]. Approximately 367 million tons of plastics are estimated to be produced by 2021, and this number is estimated to increase to 33 billion tons by 2050 [
3]. Therefore, plastic pollution has become an increasingly global concern [
4,
5], particularly microplastics (MPs), that is, plastic particles ranging between 1 μm and 5 mm [
6], which constitute a predominant form of plastic litter in the marine environment [
7,
8]. Plastics discharged into freshwater streams are often transported to the sea [
9,
10,
11,
12,
13], where they accumulate in large quantities in both the water column and the sediments [
14,
15,
16,
17].
Microplastics of primary origin are those produced intentionally at the microscopic scale as precursors of other products or for direct use as abrasives in cleaning and aesthetic products [
18]. They include microbeads, which are small plastic spheres that often range between 5 μm and 1 mm. They are composed of various plastic polymers [
19] and are included in several personal care products [
19,
20,
21]. Because microbeads are designed to be washed and carried into drains and their large-scale production, microbeads are considered potential contaminants in the marine environment [
19].
However, according to Piccardo et al. [
22] and Albanit et al. [
18], there is another category of primary MP that is almost completely ignored today: glitter particles. The glitter particle is formed by a set of plastic layers covered by thin metallic layers, similar to a sandwich, as described by [
23]. These include a variety of small, plain, and reflexive particles used in craftwork, textiles, and cosmetic products [
8]. These particles have some similarities to microbeads; however, they have not received appropriate attention from the scientific community and society as potential contaminants [
8,
18,
22,
23]. According to Provenza et al. [
24], glitter may be a model for MPs and can be considered a “symbol of microplastic” comprising all the hazardous characteristics of MPs.
Glitter is widely used in makeup, clothes and fancies, carnival floats, body paints, nail polish, craft products, and other materials [
18,
25]. It was also included in a list of polymer-based materials that were intentionally produced as MPs, according to the European Chemicals Agency [
26]. Glitter particles are carried into domestic wastewater and then released into natural aquatic environments [
23]. Albanit et al. [
18] also stated that urban drainage may represent an additional route for glitter entering the environment. Tagg and Ivar do Sul [
23] stated that glitter could be a good indicator of sewage in marine waters. Raju et al. [
27] estimated the daily input of glitter particles from a wastewater treatment plant to be 2.7–3.0*10
7 particles/day.
Glitter particles have been reported in sewage sludge samples from riverbed sediments of North England [
28,
29], samples from a wastewater plant located in Norway [
30], and sediments from UK rivers [
28]. Moreover, as increasing amounts of MPs have been found in aquatic environments worldwide [
31], the quantity of glitter may follow this trend. In a review, Yurtsever [
8] identified studies reporting the presence of glitter in aquatic environments and addressed the potential environmental hazards associated with glitters.
However, glitter particles have historically been overlooked as environmental contaminants [
2,
22,
23,
24,
33]. Although some recent studies have investigated the potential environmental impacts of glitter, very little information is available on the potential effects of glitter on marine biota, particularly neotropical organisms. Green et al. [
32] compared the ecological impacts of conventional polyethylene terephthalate (PET) glitter (non-biodegradable) with glitters made of alternative materials on the biodiversity and functioning of freshwater ecosystems and found that all types of glitters tested could cause adverse effects on aquatic ecosystems. More recently, Provenza et al. [
24] reported that ingestion of glitter by the bivalve
Mytilus galloprovincialis induced biochemical alterations, whereas Piccardo et al. [
22] reported that glitter leachates caused toxicity in several aquatic organisms. Pramanik et al. [
2] observed that exposure to glitter particles caused several disturbances in adults of brine shrimp
Artemia salina, while Albanit et al. [
18], in a preliminary study with neotropical organisms, showed that glitter leachates could case reduction of embryonic development in sand-dollars.
The toxicity associated with microplastics, including glitter, has been attributed the addition of a range of chemicals to plastic polymers during their production [
18,
25], although little is known about the composition and effects of plastic additives on aquatic biota [
22]. According to these authors, such additives include stabilizers, flame retardants, antistatics, plasticizers, lubricants, and biocides. In the case of glitter particles, the authors also mentioned the relevance of dyes; however the possible substances included in this category are not known. Therefore, efforts to determine the chemicals responsible for microplastics toxicity are relevant. The toxicity identification and evaluation (TIE) approach has been applied to complex matrices, such as effluents and sediments, to identify substances that contribute to toxicity [
33,
34]. The TIE approach involves a series of physical and chemical manipulations of samples that may cause a decrease, an increase or transformations in the bioavailability of different toxic groups [
35]. Such manipulations are followed by toxicity tests to detect the chemicals responsible for the toxicity [
36,
37].
Considering that glitter particles are globally widespread [
8], and that incipient data indicate that they can be toxic to aquatic biota, ecotoxicological studies aimed at estimating their toxic potential to marine biota are required. This study evaluated the toxicity of dispersions obtained from green and white glitter particles on embryonic development of the sea urchins
Echinometra lucunter,
Arbacia lixula, and the mussel
Perna perna. In addition, we used the Toxicity Identification and Evaluation (TIE phase 1) approach to identify possible chemicals related to toxicity.
4. Discussion
Glitter particles consist of particular types of microplastics in addition to their metal layers [
23], and they can have been reported as environmental contaminants. Recently, oyster and mussel individuals collected from mollusk farms located in southern Brazil presented glitter particles in their soft tissues [
55]. According to Campanale et al. [
56], microplastics can contain two types of chemicals: (i) additives and polymeric raw materials originating from plastics and (ii) chemicals absorbed from the surrounding environment. In the case of the glitter used in the present study, only chemicals from the first group were relevant. In this sense, our results show that glitter may release metals into the overlying water, reinforcing that glitter may be a geochemical carrier of potential contaminants. Capolupo et al. [
57] showed that leachates from microplastics presented a range of substances that were capable to cause adverse effects on the bivalve
Mytilus galloprovincialis.
Moreover, the composition of both white and green glitters, given by both Py-GC/MS analysis and manufacturer information, provides information about substances that can be potentially leached (Table SM 2), although such a list of potential substances can be larger, as addressed by Albanit et al. [
18]. The release of chemical substances from plastics has been reported previously [
58,
59,
60,
61,
62,
63]. The chemicals listed in the glitters studied herein include a set of compounds such as propylparaben (PPB), butylated hydroxytoluene (BHT), methyl paraben (MeP), methyl acrylate (MA), benzene, and toluene, in addition to the Ag measured in the filtrates.
PPB has been used to extend the shelf life of personal care products [
18], but can leach into the water and cause endocrine disruption in exposed organisms [
64], leading to a reduction in reproductive rates and embryo development. PPB affects the growth, reproduction, physiology, and gene expression of the nematode,
Caenorhabditis elegans [
65]. In turn, BHT has been used as an additive to improve the durability of plastics. Although it is considered safe for humans at the levels used, there is some controversy regarding its toxicity to aquatic organisms [
66], as it has been reported to be toxic to zebrafish embryos (
Danio rerio) at low concentrations [
66,
67]. Albanit et al. [
18] stated that BHT likely cause similar effects on marine organisms. MeP is widely used in cosmetic products [
68] and is considered toxic to both zebrafish larvae and adults [
69], as it can cause oxidative stress and endocrine disruption [
70]. Methyl acrylate (MA), identified by Py-GC/MS in white glitter [
18], has also been reported to be toxic to fish and invertebrates [
71]. These authors observed lethal effects on rainbow trout (
Oncorhynchus mykiss)
, sheepshead minnow (
Cyprinodon variegatus),
Daphnia magna, and
Mysidopsis bahia. Other two compounds identified in the white glitter, benzene and toluene, were described as toxic for the fathead minnow
Pimephales promelas [
72], especially during the first stages of development. Ag ions and Ag-based compounds are known to be toxic to a range of organisms [
73,
74]. Specifically, the Ag ions from the AgNPs interfere with the phosphate of DNA, stimulating DNA condensation and leading to a loss of replication ability in bacterial cells [
75]. Ag ions act on multiple targets within cells, leading to apoptosis [
76]. Thus, the chemicals present in glitter particles could cause toxicity to exposed organisms.
In fact, our results showed that the embryos of
P. perna,
A. lixula, and
E. lucunter were adversely affected by exposure to both types of glitter. In general,
P. perna embryos were more sensitive than sea urchin embryos (
Figure 1,
Table 2). These results are comparable to those obtained by Albanit et al. [
18], who analyzed the toxicity of leachates of both white and green glitters on embryos of the sand-dollar
Mellita quinquiesperforata; these authors also observed highly variability of toxicity, which was attributed to some factors, such as particles’ aggregation, which influences the amount of leached substances in the water. Previous studies have reported that microplastics often form aggregates in aquatic environments, although such phenomena are not well understood [
77,
78]. Microplastic aggregation likely determines their behavior and overall fate in aquatic environments [
79], including the release of substances and associated toxicity. Because microplastics aggregation may be influenced by multiple factors [
77], the resulting toxicity to aquatic biota can vary widely [
80,
81]. Moreover, differences in particle sizes may have influenced the dispersion preparation and toxicity, as reported by Albanit et al. [
18]; white glitter was easily mixed in the seawater, whereas green glitter formed a layer on the water surface.
Our results are corroborated by recent studies on the toxicity of glitter. Piccardo et al. [
22] analyzed the toxicity associated with leachates of different types of glitter, showing worse effects on marine organisms, such as embryos of the sea-urchin
Paracentrotus lividus. Exposure to glitter also caused oxidative stress in adults of the mussel
Mytillus galloprovincialis [
24] and brine shrimp
Artemia salina [
2]. Green et al. {32] compared the toxicity of leachates obtained from different types of glitter and observed toxicity to
Lemma minor, regardless of the type of glitter, and the effects were attributed to the substances present in the leachates.
In our study, both glitter dispersions caused toxic effects on the embryos of the species tested, possibly because the chemicals leached in the aqueous medium. The TIE approach showed that volatiles, oxidant substances, and metals contributed to the observed toxic effects. This result is supported by chemical information, as benzene and toluene are volatile and toxic [
72], and the toxicity of Ag is widely known, as previously discussed in this manuscript [
74]. In addition, the degradation of plastics in aqueous media can generate oxidant substances and reactive oxygen species [
82,
83] as well as the degradation of some associated organic compounds, such as parabens [
84]. Our results suggest that the degradation of glitter (and likely other plastic particles) may generate toxic by-products, and this process needs to be further investigated and understood.
Author Contributions
Conceptualization, D.M.S.A. and C.C.R.; Methodology, L.F.A., P.H.P.M., V.S.N., F.T.S., K.F., M.U., O.P.O.M., and C.C.R.; software, D.M.S.A and C.C.R.; Validation, D.M.S.A., O.P.O.M., and C.C.R.; Formal Analysis, D.M.S.A.; Investigation, D.M.S.A., L.F.A., P.H.P.M., V.S.N., F.T.S., K.F., M.U., O.P.O.M. and CCR.; Resources, D.M.S.A., C.C.R. and O.P.O.M.; Writing—original draft preparation, D.M.S.A. and C.C.R.; Writing—review and editing, D.M.S.A.; Supervision, D.M.S.A.; Funding Acquisition, D.M.S.A. All authors have read and agreed to the published version of the manuscript.