Agriculture can be related to the generation of enormous amounts of dust, of which organic dust from agricultural activities is the primary source of endotoxin. The endotoxin concentration is a significant concern in agricultural operations and sectors because the exposure value exceeds the recommended threshold value. The occurrence of endotoxin in different animal housing, food processing and other agricultural industries, such as hemp and cotton, are presented in Table 2, Table 3 and Table 4. The location of dust measurements was inside the farms or industries.

There is a variation in the occurrence of endotoxin in agricultural settings. This variation may be due to different sources of dust in agricultural settings. The harvesting of crops (nuts) using a mechanical harvester results in a higher concentration of dust [81,82]. Endotoxin has a significant correlation with the temperature [60,82,83]. The endotoxin concentration increases with an increase in the temperature [82] and relative humidity [60,84,85]. The endotoxin concentration is significantly higher on warmer days than on cold days [86,87]. In poultry and swine buildings, there is an increase in the dust and endotoxin concentration on winter days as ventilation is reduced to conserve heat [88]. The concentration of endotoxin in dust decreases due to the growth of fungi and bacteria in the livestock feed in poultry and swine farms [66]. The animal feeds may contribute to endotoxin contamination, but the major source of endotoxin inside animal houses is animal feces [88,89].

Endotoxin assessments depend on different sampling, extraction and analysis procedures followed [24]. The endotoxin concentration is higher during livestock farming than during crop farming [81]. The endotoxin concentration increases with an increase in the density of animals that are reared (pig) and a reduction in the frequency of cleaning in swine houses [88]. The concentration of endotoxin depends on the duration of exposure [88] and the type of workplace [90].

Any structure that houses livestock is certain to produce dust. Dust can be generated from feed, excreta, feathers, fur etc. The occurrence of endotoxin in animal housing around the world is presented in Table 2. The animals and workers are exposed to different levels of dust in animal housing. The floor-housed poultry rearing system in Canada has the highest level of total dust (9.56 mg/m³) [48]. The cage-housed poultry system has lower dust concentrations due to the fact that the poultry is kept in the layer system and the poultry cannot perform dust bathing on the floor, which reduces the dust. The endotoxin concentration was found to be lower in the floor-housed poultry rearing system than in the cage system. In a floor-housed poultry rearing system, the excreta are collected in the floor and the moisture is absorbed by the bedding material, which is not the case with the cage-house poultry rearing system. The inhalable dust concentration in poultry farms of Denmark has a dust concentration of 5.7 mg/m³, which is above the permissible exposure limit [91]. In the case of the swine/pig farms, the dust generated was found to be in the range of 0.128 [92] to 5.0 mg/m³ [21] and the geometric mean of endotoxin concentration varies from 16.261 [93] to 1500 EU/m³ [94] The reason for higher endotoxin levels is due to concentrated animal feeds.

In dairy farms, the dust and endotoxin concentrations were measured at the milking section and feeding sections and in free stall dairy farms. The geometric mean of the dust concentration varies from 0.2 [96] to 1.7 mg/m³ [97], and the endotoxin concentration varies from 128 [98] to 448 EU/m³ [91]. The lowest concentration of dust was observed in a mink farm (7 mg/m³) [95], and the highest concentration of dust was reported in horse stables of the Netherlands (95 mg/m³) [102], and the endotoxin concentration was 214 [95] to 555 EU/m³ [102]. The endotoxin and dust concentrations were higher in pig farms than in cattle and poultry farms due to the higher density of animals and use of concentrated feeds in pig farms. Environmental factors, such as temperature, relative humidity and wind velocity, affect the levels of airborne endotoxins at the farms [82,90,103]. Endotoxin exposure is higher for persons living in rural regions with intense livestock production [10].

In food processing industries, water is used while processing the food. Endotoxin varies with the pre-processing methods used in food processing plants. Dry pre-processed methods (sun dried cherries of coffee) result in higher concentrations of endotoxin than wet pre-processed food processing methods by using water to depulp coffee cherries [104]. The occurrence of endotoxin in food processing industries around the world is presented in Table 3. The presence of water helps to reduce dust and endotoxin exposure to the workers, as the dust gets absorbed in the water [24]. Yang, 2013, reported that the total suspended dust increases on colder days [66].

Byssinosis is commonly developed in workers who are exposed to cotton dust [5]. In rice mills, dust can be generated due to abrasion of the paddy. The occurrence of endotoxin in other agricultural industries around the world is presented in Table 4. During the post-harvest handling of cereal/fruit crops, dust is generated due to the breaking of plant materials. The workers are exposed to this contaminant and are exposed to dust, which can reduce the forced vital capacity of the workers [28,33,35,36,37,38,39]. Many researchers have collected data on inhalable, thoracic and total dust, but very few researchers have sampled the respirable fraction of dust samples [88,92,101,110]. The respirable dust fraction can penetrate beyond the terminal bronchioles of the lungs [28,41]. Respirable dust laden with endotoxin can cause serious health issues for the workers.