It should be noted that the mycelium specimen under 98 % RH reached the maximum mass gain around the seventh day in the sorption test, and after that underwent mass loss and showed signs of mould growth on the surface. As a result, maximum mass gain instead of equilibrium mass is used to calculate the equilibrium moisture content at 98 % RH as shown in Fig. 6. The equilibrium moisture content under the desorption process is only slightly higher than the adsorption process, and no significant variation between both curves for all samples. Thermogravimetric analysis of the samples is shown in Fig. 9. All four samples are thermally stable up to about 200 ◦C, and thereafter start to decompose and reach their maximum rate of weight loss between 300 and 350 ◦C. It is, therefore, necessary to protect these insulation composites from fire hazards with other fire and heat resistant components, e.g. bricks, sheathing boards, etc. The decomposition process of the samples follows a similar trend, corresponding to hemicelluloses being pyrolyzed in the range of 200 and 300 ◦C, depolymerized cellulose in the range of 300 and 350 ◦C, lignin components pyrolyzed in the range of 225 and 450 ◦C. For cork composite, depolymerization of suberin appears between 400 and 500 ◦C. The second peak at 400 ◦C is also observed on the grass composite, contributed by other recycled materials mixed in the composite. Likewise, a similar small peak can be noticed for the hemp composite where recycled materials are also used. All composites end their volatile emissions at around 450 ◦C with a remaining char residue of around 20 to 30 % of the original dry weight. Based on the thermal conductivity findings in Fig. 7, the insulation thickness for both wall types and all four studied insulation materials are formulated to achieve an overall R-value of 4.7 K⋅m2⋅W− 1 as per the Dutch requirement for an exterior wall in a residential building, or equivalent to a U-value of 0.205 W⋅m− 2⋅K− 1. The thicknesses are listed in Table 4,cannabis grow system and it can be seen that all four materials require a higher wall thickness in comparison to reference Cellulose insulation material.
The transient thermal transmittance U-value of the investigated insulation materials under two different wall types and six different climates are investigated and summarized in Fig. 10. Only transient Uvalues in the ‘heating period’ from October to March are included as the U-value under warmer months will yield non-sensible results and is not of interest in this study. In general, all four insulation materials display matching trends of transient U-value under a combination of the same climate and wall type, however, diverge significantly when compared across different climates or wall types of the same material. Under continental climate Dfa , Dfb and Dfc , the insulated walls provide uniform thermal insulation performance close to the designed U-value at 0.205 W⋅m− 2⋅K− 1 in the heating period. Higher transient Uvalues however are observed on the walls under temperate climates Cfa , Cfb and Cfc , coincide with their milder and wetter climate profiles. On the whole, the insulated timber frame walls perform better than the brick walls, in particular under temperature climates, when a similar initial designed U-value is set for all cases. This is a consequence of the thicker and denser brick layers which hamper the moisture transport in the wall assemblies, causing higher moisture accumulation in the insulation material. This pattern reaffirms the central role of exterior climates and type of building envelop design in the evaluation of building insulation performance, when a similar category of insulation materials are to be considered, in this case, the bio-based insulation materials. If without considering durability aspects from potential deterioration due to mould growth under a humid environment, or no concern of overall wall thickness owing to the thickness of insulation layer required for the intended U-value, there is no specific material to be recommended based on their transient U-value performance. However, when the wall thickness is of interest, the cork composite with its less demanding thickness requirement is the preferred selection compared to other investigated bio-based materials, followed by the grass composites. The equilibrium moisture content in the investigated bio-based insulation composites under two different wall types and six different climates in a simulated year is shown in Fig. 11.
Mycelium composite shows the highest moisture content under all climates and wall types, while cork composite shows the lowest and the most regulated moisture content throughout the year in general. Both grass and hemp composites exhibit similar moisture content to the reference cellulose insulation material. These dynamic moisture content of the composites are in agreement with their sorption isotherm, i.e. higher sorption capacity of mycelium composite and the opposite for cork composite. Higher moisture content in an insulation layer can be found at the near-interfaced layers, in the case of the selected wall type and climates, they are either at layers next to the exterior sheathing board or behind the interior sheathing board.A few observations can be generalized based on the climate types: for Cfa and Dfa , moisture tends to accumulate at the exterior interface during the winter period and interior interface during the summer period; for Cfb , Dfb and Dfc , moisture accumulation is generally found on the exterior interface during the winter period, and while the moisture content is increasing on the interior interface during summertime it is still not exceeding that of the exterior side; and for Cfc , the moisture content at the exterior interface is always higher than the interior interface. It can be established that the insulation layer at the exterior interface has the highest averaged moisture content under all six climates, and consequently is most likely subjected to mould growth and degradation compared to other parts of insulation under different climate conditions. In terms of wall type, insulation material inside the timber frame walls have generally lower moisture content at the exterior interface than those inside brick walls across different climates except Dfc. The opposite trend is observed at the interior interface where the insulation layer in timber frame walls has higher moisture content compared to brick walls. Note that no vapour retarder is included in the design of all simulated walls to retard the vapour diffusion process, and a ventilated air cavity is included in all cases to provide additional hygrothermal regulation to the overall wall assembly. After exposing the test specimen for four weeks to high humidity in a desiccator filled with water, the specimen is visually inspected with the naked eye and microscope for the presence of mould. Fig. 13 shows photos taken on the specimen with and without high humidity conditioning. The fungal growth on the test specimen is assessed according to ISO 846 and the intensity scales of mould growth are assigned to them in Table 5. Note that mould growth was already observed on mycelium composite conditioned under 98 % RH in the sorption test, as discussed in section 3.1.
Discolouring on the hemp composite can be perceived with naked eyes and fungi are distinguished easily under a microscope. For the grass composite, no obvious mould growth or discolouring is observed with the naked eye, however, deterioration of the fibres is noticeable under the microscope. No apparent deterioration, mould growth or discolouring is detected on the cork composite. These results are in agreement with the literature: similar mould development can be distinguished with the naked eye on the mycelium-miscanthus test sample by Dias et al.; fungi contamination can be observed under a microscope on hemp shiv composites by Viel et al.; on the other hand mould development on grass and cork composite is not presented on the literature. Marijuana smoke is a complex mixture composed of thousands of chemical compounds,many of which are qualitatively similar to those found in tobacco smoke.Like tobacco smoke,marijuana smoke has been associated with numerous adverse pulmonary effects in humans including airway inflammation,chronic bronchitis,edema,mucus hypersecretion,and the impairment of large airway function and lung efficiency.Moreover,Aldington et al.showed that the impairment of large airway function and lung efficiency is 2.5–5 times greater in marijuana smokers than tobacco smokers.Like tobacco smoke,previous studies have also shown marijuana smoke to be genotoxic both in vitro and in vivo.In addition,it is suspected that marijuana smoke may be carcinogenic.Indeed,some agencies such as the California Environmental Protection Agency have placed marijuana smoke on their list of chemicals known to cause cancer.However,since there is a paucity of marijuana-only smoking populations to complete definitive studies,epidemiological studies conducted to date are limited in scope,and often confounded by concurrent tobacco smoking.Therefore,a clear and widely accepted empirical link between marijuana smoking and cancer does not exist.Information on the pharmacokinetics of marijuana smoke,and the mechanisms by which it may cause adverse effects,is also limited.Several mechanisms have been proposed including genotoxicity,alterations in endocrine function,alterations in cell signaling pathways,marijuana grow system and immune suppression.However,many of these findings are based on the testing of individual cannabinoids found in marijuana smoke,as opposed to the whole smoke or smoke condensate.
Genome-wide expression profiling may provide information to permit a better understanding of the toxicological pathways perturbed by exposure to marijuana smoke.Currently,there are no published studies that have used a whole genome toxicogenomics approach to evaluate responses to marijuana smoke.However,Sarafifian et al.employed a targeted stress response gene expression array to evaluate the effects of 9-tetrahydrocannabinol,the main psychoactive component of marijuana,on human small airway epithelial cells.They observed significant changes in genes related to xenobiotic metabolism,DNA damage response,inflammation and apoptosis.micro-array technology has been used more extensively to evaluate gene expression changes following exposure to tobacco smoke.For example,Sen et al.reviewed 28 studies examining transcriptional responses to complex mixtures including whole cigarette smoke and cigarette smoke condensate,and included in vivo and in vitro studies using human and rodent tissues.It was determined that the pathways most frequently affected by tobacco smoke were oxidative stress response,xenobiotic metabolism,inflammation/immune response,and matrix degradation.Other micro-array studies have noted a DNA damage response leading to cell cycle arrest and apoptosis to be among the top pathways affected by tobacco smoke.The results of this study showed extensive overlap with the affected pathways highlighted in the review by Sen et al..Our study also showed that gene expression is remarkably similar across cigarette brands,and there is limited variation in the genotoxic potency of cigarette smoke condensates.In contrast to these findings,our earlier work revealed that tobacco and marijuana smoke condensates differ substantially in terms of their genotoxicity.More specifically,MSC were observed to be significantly more cytotoxic and mutagenic than matched tobacco smoke condensates.In addition,TSC appeared to induce chromosomal damage in a concentration-dependent manner,whereas matched marijuana condensates did not.The mechanisms underlying these differences in toxicity are unclear and warrant further investigation.As an extension of our previous work,the objective of the present study is to employ a toxicogenomics approach to compare and contrast the molecular pathways that are perturbed by MSC and TSC.A murine pulmonary epithelial cell line was employed for in vitro exposures to both MSC and TSC.The results show that the pathways perturbed by MSC as compared to TSC are largely similar.However,subtle differences in gene expression provide insight into mechanisms underlying the observed differences in toxicities.The tobacco samples consisted of a popular Canadian brand of fine-cut tobacco obtained from a local retail store.The cigarettes contain Virginia flue-cured tobacco,which is distinct from the mixed tobacco blends typically found in American cigarettes.The cannabis samples consisted of a standardized product,grown under strictly controlled and documented conditions.The product was obtained from Prairie Plant Systems Inc.,and all samples were from harvest #55.Upon harvest,flowering heads were dried to a moisture content of approximately 10%,milled to 10 mm,packaged and irradiated.The preparation and combustion of the cannabis and tobacco cigarettes was conducted by Labstat International Inc.as described previously.Briefly,samples of marijuana and tobacco were laid out on aluminum trays and conditioned at a temperature of 22 ◦C and a relative humidity of 60% for 48 h.775 mg of each product was transferred to a cigarette-rolling device,and cigarettes were prepared using commercially available cigarette papers,all without filters.All cigarettes were stored in sealed plastic bags until combustion.Samples were removed from the bags and conditioned for a minimum of 48 h prior to smoking,as required by ISO 3402:1999.The cigarettes were smoked according to a modified smoking regime intended to reflect marijuana smoking behavior.