The number of pet animals in the European Union (EU) is increasing. Pet dogs (in the following, referred to as dogs) are growing in popularity with 66.4 million dogs in the EU in 2017 compared to 63.7 million in 2016 [1
]. In Germany, for example, the number of dogs increased from 5.5 million in 2005 to 9.2 million in 2017 [2
]. Naturally, a higher number of dogs also leads to a rising amount of consumed pet food, and a higher total volume of urine and feces. Particularly, the latter may lead to direct environmental impacts. For example, the urban and rural flora is affected by urine, making trees become more prone to diseases, etc. [3
]. Often, this is visible in big cities, where the density of population and pet animals is high and (green) space is limited.
A few LCA studies assessing potential environmental impacts related to pets and dogs are already available. However, they focus only on specific environmental impacts or on specific life cycle stages or processes, such as pet food [4
]. Moreover, within the Product Environmental Footprint (PEF) initiative [10
] a PEF pilot study was conducted aiming at analyzing potential environmental impacts of pet food for dogs (and cats) and developing product environmental footprint category rules (PEFCR). The PEFCR provide guidance on how to conduct a PEF study (basically an LCA based study) for pet food [12
]. They considered the production and transportation of pet food, as well as the end-of-life (EoL) of the packaging and food waste. Not addressed, i.e., out of the scope of this PEF study, is the EoL of the pet food after its consumption. The full life cycle of pet food is, hence, not considered. To the knowledge of the authors, there is no LCA study available, which comprehensively addresses potential environmental impacts related to dogs from a total life cycle perspective.
The goal of this paper is, therefore, to conduct an LCA case study of a dog, to comprehensively analyze potential environmental impacts, identifying hotspots and improvement potential. This study is of interest to the LCA community, because it connects to and complements existing studies, focusing on parts of the dog´s life cycle, particularly the PEF study for pet food.
3. Results and Discussion
In the following, the results of the case study on a dog are presented and discussed. Shown are: The absolute values of the LCIA per impact category (Section 3.1
), the relative contributions of life cycle stages/ and processes to the impact categories (Section 3.2
), the LCIA results normalized to the EU domestic market (Section 3.3
), and the results of the scenario analysis (Section 3.4
3.1. LCIA Results: Absolute Values
The absolute values of the LCIA results for the impact categories can be seen in Table 4
. The results are shown for an average dog of 15 kg, a life expectancy of 13 years, and an assumed average pick-up rate of feces of 15%.
To evaluate the results shown in Table 4
and to illustrate their significance, in the following, some examples are provided which compare the impacts caused by a dog with impacts caused by common products or activities or an average German citizen.
Over the whole lifetime of 13 years an average dog causes around 8.2 t CO2
eq. This almost equals the amount needed to produce Mercedes C250 middle-class luxury car [24
]. In one year, a dog emits around 630 kg CO2
eq, which equals around 7% of the annual greenhouse gas (GHG) emissions of an average German citizen (in 2016 around 11.1 tons CO2
eq were emitted per capita in Germany [25
]). Moreover, the total amount of GHG emissions caused by a dog are similar to the amount of GHG emissions caused by driving around 72,800 km with a car (assuming that the car emits around 120 g CO2
eq. per km) or by 13 return flights from Berlin to Barcelona [26
]. The freshwater ecotoxicity potential caused by a dog is around 18,000 CTUe. That is more than freshwater ecotoxicity potential caused by treating 6.5 ha arable land for one year with the herbicide glyphosate (according to [27
] around 2.8 kg of glyphosate are used per ha per year, which equals a freshwater ecotoxicity potential of around 1500 CTUe). The total freshwater eutrophication potential of a dog is around 5.0 kg P eq., which would equal the eutrophication potential caused by producing 21,900 l of beer [28
]. These examples obviously do not intend any comparison between these rather different products, they just serve the purpose of providing a reference for an understanding of the orders of magnitude of the impacts of a dog.
3.2. Relative Contribution of Life Cycle Stages
The contribution of the different life cycle stages/processes within the product system of a dog to the total result is displayed in Figure 2
. Except for the impact categories of freshwater eutrophication potential and freshwater ecotoxicity potential, the main contribution to all the impact categories comes from the life cycle stage pet food. Here, the impact in most categories is mainly caused by the processes ´ingredients´ and ´packaging production’ [12
]. The category of freshwater eutrophication is mainly determined by the dog´s urine (around 44%) and the dog´s feces (around 43%). This is mainly caused by phosphorous contained in the excrements. Urine does not contribute significantly to any other category, while feces have a significant contribution (around 50%) also to the category of freshwater ecotoxicity potential. Impacts related to the plastic bag production are visible in the category of water depletion potential (around 9%). Impacts related to the waste collection step are not visible in several categories but never exceed 5%. Relevant contributions of the EoL stage, which, in Figure 2
, include the incineration and landfill of municipal waste, can be seen only for the category of climate change potential (around 7%). The negative values in the impact category water depletion result from credits provided for waste treatment/incineration in the EoL stage due to energy recovery.
3.3. Normalized LCIA Results
Normalization is an optional step of LCIA, which allows the practitioner to express the results using a common reference value [29
]. For this study, we chose the European domestic market as a reference impact and used the normalization factors (NF) provided by the European Commission (EC) in the context of the European Environmental Footprint [30
]. Normalization factors express the total impact occurring in a reference region for certain impact categories within a reference year. Using these factors, the LCIA results of this case study can be presented as a fraction of all emissions in the EU per year or also as a share of all emissions of an average EU citizen.
When evaluating normalized results, it has to be noted that the NFs, i.e., the determined numbers of total emissions, have different robustness levels. The EC [30
] differentiates between the levels low, medium, high, and very high based on the data availability of the emissions and the methodological development of the LCIA methods. Generally, normalized LCIA results, and particularly those which are calculated using NFs with low robustness levels, need to be interpreted carefully.
Due to the difficulties related to normalization, Figure 3
shows the normalized results of the case study only for three selected impact categories: Climate change, the only impact category (next to particulate matter), which is characterized with a very high robustness level, according to [30
], and freshwater eutrophication and freshwater ecotoxicity. Though the latter two categories are characterized with medium to low and low robustness level, we decided to show their normalized results because both categories are highly influenced by the dog´s excrements. The normalized results in Figure 3
are expressed as fraction per EU citizen, i.e., the results for the individual impact categories are all compared to the annual impact of an average EU citizen. Moreover, MFR resource depletion, as well as human toxicity cancer and non-cancer effects, has large fractions, but as those impact categories are mainly driven by the pet food, they are not displayed in Figure 3
. The normalized results for all impact categories can be found in the Supplementary Materials (Figure S1)
To illustrate the meaning of the normalized results, we use the following example: The total LCIA results of one dog over 13 years shown in Table 4
correspond to an annual impact of around 630 kg CO2 eq. For comparison, the GHG emissions in the EU in 2010 were about nine tons CO2 eq. per person [30
]. Therefore, one dog has an impact of 630/9000 = 0.07 person-year, which means that the impact of an average dog is around 7% of an average EU citizen in a year similar to the one calculated for an average German citizen in Section 3.1
High fractions per EU citizen of more than 15% up to 26% were calculated for the categories of freshwater ecotoxicity and freshwater eutrophication (reference values in [30
]). It is not clear here if the high normalization results indeed represent high fractions or if the results are only high because the NFs are too small. This could happen if not all emissions related to this impact category, for instance, direct emissions caused by dog excrements, are captured in the NFs. However, in any case, the contribution of a dog to these impact categories appears to be rather significant.
3.4. Scenario Analysis
shows the results of the scenario analyses examining the influence of both the weight of a dog and its life expectancy on the LCIA results (see Table 3
Naturally, the impacts caused by one dog increase with its life expectancy with increasing weight. Regarding life expectancy and its impacts, a linear relation was assumed. For illustrating the influence of life expectancy and weight/size of the dog, we used two scenarios representing two extremes: A small dog of 7.5 kg with a low life expectancy of eight years and a big dog of 30 kg with a high life expectancy of 18 years.
Compared to the impacts of the average 15 kg dog caused during its 13-year lifetime (e.g., 8200 kg CO2 eq.) the impacts caused by a small 7.5 kg dog that lives eight years would be less than a half of it (e.g., 3000 kg CO2 eq.) while the impacts caused by a big 30 kg dog that lives 18 years, would be more than twice as high (e.g., 19,000 kg CO2 eq.).
For most impact categories in the 0% pick-up scenario, the deviation of the results of the 15%-pick-up scenario (average scenario) is negligible (less than 1%). Only within the categories of freshwater eutrophication and freshwater ecotoxicity, significant differences between the results can be seen. The impact increases almost 9% in the category of freshwater ecotoxicity, a category where feces have a high contribution to the overall impact, derives from more direct emissions (from feces) that enter the environment. Feces also have a high contribution to the category of freshwater eutrophication (7.5%).
In the 100% scenario, significant changes in the results can be observed in the same categories as in the 0% pick-up scenario. If all feces are picked up, there are (almost) no direct emissions from feces, which is one of the main drivers in freshwater eutrophication and freshwater ecotoxicity (see Figure 2
). This also leads to significant decreases in both categories (−43% and −50%).
4. Conclusions and Outlook
This study analyses the potential environmental impacts of a pet dog, taking into account impacts related to its food and excrements, i.e., trying to address the whole ´life cycle´. The following conclusions are mainly valid for a German or European context, but potentially also other developed countries. Regional differences in feeding dogs and treating their excrements were not part of this study.
The life cycle stage ´pet food´ is the main contributor to all impact categories except of those that are affected by direct emissions, i.e., the dog excrements, such as freshwater eutrophication and freshwater ecotoxicity. The impacts in these two categories are mainly determined by dog urine and feces. When looking at the whole life cycle, the impact caused by the production of plastic bags is comparably small. In this study, the calculation assumed two bags per day, hence, rather overestimated the real number of bags needed to collect the feces, only one impact category was affected by more than 8%. Waste collection and waste incineration only have visible impacts in the categories of climate change and water depletion.
The results obtained for the category of climate change potential in this study are overall in line with those calculated by [4
], and also in this study, the main contribution to climate change comes from pet food. It has to be noted, that both studies differ regarding their system boundaries: In contrast to this study, [4
] considered drives with the dog, nurturing, toys, and other accessories next to the pet food, but excluded the EoL emissions of excrements. In that sense, these studies contain complementary aspects. However, at least for climate change, the additional aspects covered by [4
] did not have a significant contribution to the overall impact, whereas the inclusion of the EoL stage in this study showed significant contributions to the impact categories of freshwater eutrophication and freshwater ecotoxicity. It should be noted, that in [4
] only global warming potential and eco-points were calculated for different pet animals. Other impact categories were not included.
As dogs urinate to mark territories and communicate [31
], the impact due to urine can probably not be reduced without harming the social structure of the dog. However, the impact of feces can be significantly reduced if feces would be collected and disposed of properly. The scenario analyses of different pick-up rates showed that collecting the feces, hence decreasing direct emissions, would lead to significant decreases in the categories of freshwater ecotoxicity and freshwater eutrophication. A positive side effect of collecting the feces would also be the reduction of littering in general, which is not measured in LCA. In Berlin in Germany, for example, special cars are used to collect feces from the streets. These cars consequently lead to a reduction of direct emissions from feces, but also cause additional impacts due to a higher collection effort.
Moreover, optimizing dog food could significantly contribute to reducing environmental impacts. According to [12
] the impacts of the pet food are mainly caused by beef and poultry co-products, tinplate production, steel can production and transport to retailer.
It has to be noted that many processes and activities related to a dog´s life, such as health care or accessories, have been excluded from this study for now. If they would have been considered, the environmental impacts would be even higher [4
It is acknowledged, that there might be potential positive impacts of dogs on human health due to interactions between dog and owner (described, e.g., by [33
]), which were not analyzed in this study, as they demand much broader system boundaries. These positive impacts have to be acknowledged when the environmental impacts are evaluated. From a purely environmental point of view, fewer pets and if at all, smaller pets are obviously preferable.
Further research and case studies should focus on the following topics:
Inclusion of other life cycle stages, e.g., consideration of accessories, care of the dog (including, e.g., pharmaceuticals).
Addressing other environmental aspects, such as littering.
Detailing the analysis for different dog breeds and types of food.
Comparison of different consumption lifestyles (with and without pets), in a broader context of, e.g., the recently proposed new Life-LCA method by [15
]. Differences may relate, e.g., to different travel behaviors.
This study is a first attempt to comprehensively analyze environmental impacts related to pet dogs. It was found that the environmental impacts of pet dogs are rather significant. Environmental hotspots were identified, some recommendations for reducing optimization potential are given, and several ideas for future research are provided.