Agrochemicals are used to improve the production of crops, but they also can contaminate the environment. Hence, there is a need for formulation with controlled release of agrochemicals to reduce pollution and health hazards [173–175]. In recent decades, there has been increasing interest in the adoption of nanotechnology for agro-industrial applications and new formulations of pesticides have been developed (Table 4.3), modifying the performance of active compounds and eventually reducing their impact on the environment [176,177]. Generally, a polymeric material has been used to incorporate pesticides or other bioactive agents into nano-based products such as nanoparticles and nanomatrices [178].
Table 4.3. Polymers of macroalgae used for developing nano-based products for delivery of agricultural inputs.
PolymerSystem (nanoemulsion/nanoparticle)ActionReferencesAlginateNanoparticle by ionotropic pregelation of alginate with calcium chloride followed by complexation between alginate and chitosanHerbicide[178
]AlginateNanoparticles were formulated by emulsion cross-linking technologyPesticide/insecticide/herbicide[184
,196
]CarragenEmulsifiersPesticide/insecticide[193
]Interestingly, according to Camara et al. [179], around 3000 patents have been registered worldwide in the last 10 years using micro- or nanocapsules containing biocides, repellents, attractants, or plant growth regulators. These formulations intend to provide the slow-release profile to the bioactive compound, reducing leaching losses and active volatilization, also increasing safety during application and being less prone to cause phytotoxicity [173–175].
Alginate is a water-soluble, anionic polymer (negatively charged polysaccharide), commonly produced by marine brown algae. It is mainly composed of α-l-guluronic acid and β-d-mannuronic acid residues linked by 1→4-glycosidic linkages. It is a nontoxic, biocompatible, biodegradable, and inexpensive compound. Thus, it is extensively used for several biological, biomedical, and food applications [180–182]. Silva et al. [178] developed an alginate/chitosan nanocarrier system for paraquat encapsulation and detected a longer period of action of the chemical, while reducing problems of ecological toxicity. Similar results were demonstrated using alginate for azadirachtin encapsulation, where a slower release profile was observed compared with the free form of the bioactive compound [183].
Kumar et al. [184] synthesized and characterized a neonicotinoid insecticide imidacloprid-loaded sodium alginate nanoparticle and further evaluated it against the pest population of leafhoppers. The results reflected that the encapsulated formulation was more effective than the pure pesticide after 15 days of application that was significantly reducing the number of insects per leaf, comparatively to the free form of the insecticide. Thus, it has been claimed that nanoformulations can reduce the amount of pesticides used along the food production chain, decreasing the amount of agrochemical residues in foods and also the risk of environmental pollution.
Another kind of algal polysaccharides includes the sulfated polysaccharides such as carrageenans of red algae, ulvans isolated from green algae, and fucoidans produced by brown algae [185–188].
Carrageenan, an anionic sulfated polysaccharide, has a straight backbone of alternating 3-linked β-d-galactopyranose, 4-linked α-galactopyranose residues [189]. Carrageenans have been claimed as a promising excipient for pharmaceutical usage. Due to its biocompatibility, strong negative charge, gelling, thickening, stabilizing, and viscosity properties, it has been extensively studied in drug delivery systems, tissue engineering, and wound healing applications [190–192].
Despite the wide utilization of carrageenans in pharma and food product formulations, their usage as a drug delivery system in other areas such as agrochemical has also been reported. For example, Westgate, Schultz, and Hazzard [193] evaluated the effects of carriers (carrageenan, vegetable, and paraffinic oils), emulsifiers, and biopesticides (Bacillus thuringiensis, spinsosad, and neem) compounds for the Lepidopteran pest control Helicoverpa zea (corn earworm) in sweet corn plants. Authors found that carrageenan carrier presented the least effect upon ear development as measured by the length of nonpollinated kernels at the tip. Additionally, the carrier–pesticide combinations that allowed obtaining the best ear quality were the insecticide spinosad in carrageenan or the corn oil and B. thuringiensis also in combination with carrageenan.
In their turn, fucoidans are widely investigated because of their various biological properties such as anticoagulant, antiviral, antiangiogenic, antiinflammatory, immunomodulating, and antitumor activities [189,194]. Ulvan is a polysaccharide composed of structural subunits of uronic acids and neutral sugar [195]. However, despite a large number of studies in the area, no reports were found on the development of formulations containing fucoidans or ulvans as drug delivery systems for agriculture, making the topic very promising for the study.
The fact that the literature presents consolidated nanosystems using algal polysaccharides for drug release in the pharmaceutical industry demonstrates the vast possibilities of using these biocomposites to develop nano-based delivery systems of active ingredients with biostimulant activity in crop species. In point of act, active nanoencapsulation in polymeric nanoparticles can reduce undesirable toxic effects in nontarget organisms and improve the thermal and photochemical stability of the biocomposite of interest, beyond the biostimulant effect that these compounds alone provide.