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sustainability
Article
Environmental Impacts of a Pet Dog: An LCA
Case Study
Kim Maya Yavor †, Annekatrin Lehmann and Matthias Finkbeiner *
Institute of Environmental Technology, Technische Universität Berlin, 10623 Berlin, Germany;
my@wip.tu-berlin.de (K.M.Y.); annekatrin.lehmann@tu-berlin.de (A.L.)
*Correspondence: matthias.finkbeiner@tu-berlin.de; Tel.: +49-30-314-24341
†first authors, equal contribution.
Received: 24 March 2020; Accepted: 16 April 2020; Published: 22 April 2020
Abstract:
The number of pet animals in the European Union is increasing over the last decades. Few
studies with a limited focus in terms of impacts and life cycle stages exist that assess the environmental
impacts of dogs. This paper addresses the entire life cycle of a dog. An LCA study on an average dog
was conducted considering the pet food and dog excrements, i.e., urine and feces. Fifteen impact
categories were analyzed. An average dog has a climate change and freshwater eutrophication
potential of around 8200 kg CO
2
eq and 5.0 kg Peq., respectively. The main contribution to most
impact categories over the dog’s life is caused by pet food. Freshwater eutrophication is mainly
determined by the dog
´
s urine and feces. Feces also have a significant contribution to the category of
freshwater ecotoxicity. Impacts increase significantly with increasing weight and a longer lifetime of
the dog as well as low collection rates of the feces. This LCA study reveals that pet dogs can have a
significant environmental impact, e.g., around 7% of the annual climate change impact of an average
EU citizen. Optimizing pet food and increasing the feces´ collection rate can reduce the impacts.
Keywords:
life cycle assessment; pets; dog; product environmental footprint; excrements; feces; urine
1. Introduction
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
–
9
]. Moreover, within the Product Environmental Footprint (PEF)
initiative [
10
,
11
] 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.
Sustainability 2020,12, 3394; doi:10.3390/su12083394 www.mdpi.com/journal/sustainability
Sustainability 2020,12, 3394 2 of 13
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.
2. Materials and Methods
This chapter describes how the LCA study was conducted, following the four phases of LCA
according to ISO 14040 and ISO 14044. The goal and scope phase are described in Section 2.1, followed
by a description of the inventory phase in Section 2.2. The phases of life cycle impact assessment
(LCIA) and interpretation are covered in Section 3under results and discussion.
2.1. Goal & Scope
The goal of this study is to identify the potential environmental impacts related to a dog. For the
study, an average dog of 15 kg was assumed. This assumption was taken from the PEF pilot study
for pet food [
11
]. Moreover, an average lifetime of 13 years was assumed [
13
,
14
]. In the following
subsections, the functional unit and the reference flow, the product system and the selected impact
categories and LCIA methods are described. In addition, the scenarios considered in the scenario
analysis are outlined.
2.1.1. Functional Unit/Reporting Unit and Reference Flow
An LCA requires defining a functional unit. For this study, it was suggested to use the term
reporting unit, which was also proposed by [
15
] for the Life-LCA approach and following the proposal
made for organizational LCA [
16
]. The reason is that it is not intended to compare functionally
equivalent dogs or even dogs with other products. Therefore, a reporting unit approach based on
simple reference flow was chosen. Hence, the reporting unit here is defined as one average dog. The
reference flow is expressed as the life of an average dog assuming an average weight of 15 kg and an
average life expectancy of 13 years.
2.1.2. Product System
The product system is illustrated in Figure 1and includes the following two main parts:
(1)
dog food, including the food’s production, transport, and EoL
(2)
dog excrements, i.e., feces and urine
Part 1, dog food, was addressed in the PEF pilot study. Information on the modeling, as well as
the results, can be found in the PEFCR for pet [
12
] and the related PEF study [
17
]. The LCIA results of
this PEF study were used as a
´
module
´
in this case study to model the process (life cycle stage) food
for the dog. What happens after the pet food has been consumed by the dog, namely that it (or parts of
it) enters the environment as urine and feces are not considered in the PEFCR and PEF study on pet
food. This part (part 2) is investigated and modeled in this case study considering the different ways
feces and urine can take: They can be directly emitted into nature or collected in bags and subsequently
disposed of in waste bins.
A detailed description of the processes included in the product system is provided in Table 1.
Further information (quantitative description and data sources) are provided in the inventory part in
Section 2.2. Not included in this study are veterinary checks and treatments of the pet, as well as care
(e.g., washing of the pet), toys, and accessories. Moreover, processes related to the creation and death
of pets are not considered. According to the study of Annaheim et al. [
4
], as well as own estimations,
these processes only contribute small shares to the overall environmental profile of the dog, i.e., their
exclusion does not significantly affect the results.
Sustainability 2020,12, 3394 3 of 13
Sustainability2020,12,xFORPEERREVIEW3of14
Figure1.Illustrationoftheproductsystemofadog.
Table1.Inputsandoutputsconsideredintheproductsystemofadog.
Input
(pet
food)
Petfooditself
productionofthepetfood,includingfoodpackagingand
transportation
Dishesforpetfood washing
Output
(feces
and
urine)
Plasticbagfor
disposal
production,includingtransportationofthebag
wastecollection
wastetreatment(landfillingandincineration)
Cleaningofstreets
water
scavenger
Directemissions
fromfecestosoil
fromurinetosoil
2.1.3.LifeCycleImpactAssessment(LCIA)CategoriesandMethods
Fortheimpactassessment,thesameimpactcategoriesandLCIAmethods(ILCD/PEF
recommendationv1.09)wereselectedasinthePEFCRforpetfood[12],whichalsocontainsthe
documentationofthespecificcharacterizationmodelsandversionsused.Thisallowedustousethe
LCIAresultsobtainedinthePEFstudyonpetfoodformodelingtheprocessofpetfoodinthiscase
study.Intotal,thefollowing15impactcategorieswereconsidered:Climatechange,ozonedepletion,
humantoxicity(cancerandnon‐cancer),particulatematter,ionizingradiation(humanhealtheffects),
photochemicalozoneformation,acidification,terrestrialeutrophication,freshwaterandmarine
eutrophication,freshwaterecotoxicity,landuse,waterdepletion,andMFR(mineral,fossiland
renewable)resourcedepletion.
2.1.4.ScenarioAnalysis
Ascenarioanalysiswasconductedtoassesstheinfluenceofthefollowingparametersonthe
overallresults:
lifetimeofthedog
weightofthedog(weightisusedheretoexpressdifferentsizesofadog)
typeofcollectingthedog´sfecesandcollectingrate
Furtherdetails(datausedanddatasources)arepresentedinSection2.2.
2.2.Inventory
Figure 1. Illustration of the product system of a dog.
Table 1. Inputs and outputs considered in the product system of a dog.
Input (pet food)
Pet food itself
•production of the pet food, including food
packaging and transportation
Dishes for pet food •washing
Output (feces and
urine)
Plastic bag for disposal
•production, including transportation of the bag
•waste collection
•waste treatment (landfilling and incineration)
Cleaning of streets
•water
•scavenger
Direct emissions •from feces to soil
•from urine to soil
2.1.3. Life Cycle Impact Assessment (LCIA) Categories and Methods
For the impact assessment, the same impact categories and LCIA methods (ILCD/PEF
recommendation v1.09) were selected as in the PEFCR for pet food [
12
], which also contains the
documentation of the specific characterization models and versions used. This allowed us to use
the LCIA results obtained in the PEF study on pet food for modeling the process of pet food in this
case study. In total, the following 15 impact categories were considered: Climate change, ozone
depletion, human toxicity (cancer and non-cancer), particulate matter, ionizing radiation (human
health effects), photochemical ozone formation, acidification, terrestrial eutrophication, freshwater and
marine eutrophication, freshwater ecotoxicity, land use, water depletion, and MFR (mineral, fossil and
renewable) resource depletion.
2.1.4. Scenario Analysis
A scenario analysis was conducted to assess the influence of the following parameters on the
overall results:
•lifetime of the dog
•weight of the dog (weight is used here to express different sizes of a dog)
•type of collecting the dog´s feces and collecting rate
Further details (data used and data sources) are presented in Section 2.2.
Sustainability 2020,12, 3394 4 of 13
2.2. Inventory
Input and output data were collected for the processes described in Table 1using the PEFR for
pet food and the related PEF study, as well as literature and assumptions, for instance, on the dog
´
s
owner
´
s behavior. In addition, we also analyzed direct emissions to the environment coming from the
excrements, i.e., nutrients and heavy metals. The following three subsections provide information on
how the processes (life cycle stages) of pet food and excretions (feces and urine) were modeled, and
how these processes varied in the scenario analysis. For the modeling, the LCA software GaBi and the
databases of the thinkstep AG (thinkstep 2017) and ecoinvent 3.5 were used (ecoinvent 2018).
2.2.1. Pet food
As described in Section 2.1, the weight of an average dog was assumed to be 15 kg. This
assumption, as well as information on its daily energy requirements and daily consumed pet food
(i.e., 883 g wet pet food), was taken from the PEFCR for pet food [
12
]. All data related to the pet
food (production, use and EoL) were taken from the PEFCR for pet food as well and the related PEF
study [17].
2.2.2. Excrements (Feces and Urine)
The environmental impacts related to the excrements of a dog and different collection and
treatment procedures have not yet been analyzed comprehensively in LCA but are modeled in this
case study. First, information on the amount and composition of the excrements is provided. Then, the
EoL of the excrements is described, which here includes the emission of excrements into nature, as
well as the collection of feces and their treatment/disposal.
Amount and Composition of Excrements
An average dog produces around 0.2 kg feces and 0.4 l urine per day. These values were calculated
by Schaepe [
18
] using data observations of three dogs on five days. Assuming an average lifetime
of 13 years, this equals to almost 1000 kg of feces and almost 2000 l of urine per dog. In this study, a
constant amount of feces and urine is assumed over the whole lifetime of the dog. This simplification
is suitable as the consumed amount of proteins of a young dog (younger than six months) is lower
than the consumption of an adult dog, but at the same time, young dogs have a higher need of fat than
their senior fellows [
19
,
20
]. As this shift in nutrition only applies to the first six months, we chose to
regard the consumed food, and thus the resulting excrements, as constant over the life of the dog.
For modeling environmental impacts related to the emission of urine, average data for its
composition provided by Schaepe [
18
] were used. Regarding the composition of feces, no data were
found. Therefore, we conducted our own analyses on samples of feces we took from three different
dogs. All dogs were between five to six years old, one dog was small (9 kg), one medium (13 kg), and
one big (18 kg). One dog ate special salt-free pet food, while the other two ate normal pet (wet) food.
The samples were analyzed with regard to the following elements: Arsenic, boron, cadmium, calcium,
chrome, cobalt, copper, iron, lead, manganese, molybdenum, nitrogen, organic substance, phosphate,
potassium, selenium, sodium, sulphur, and zinc. A detailed list of the composition of the dog
´
s feces
and urine is included in the Supplementary Materials Table S1.
It should be noted that the sample size for determining the feces data was relatively small. As
shown by Meyer et al. [
19
], different breeds of dogs and different diets have obviously an influence
on the composition of excrements. However, no comprehensive feces composition with such a high
resolution is available. Therefore, the data used are the best available, but future studies should check
the representativity for a range of dogs with different types of food.
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EoL of Excrements
The EoL of excrements was considered as follows: Regarding the urine, it was assumed to be
completely emitted to soil, as the urine cannot easily be collected or disposed of differently. Hence,
urine was considered as direct emission into nature and calculated in this case study based on the
composition listed in the Supplementary Materials Table S1.
Regarding the feces, the following differentiation was made (see also Figure 1):
•
feces are picked up in plastic bags by the dog
´
s owner and disposed of in municipal waste bins
(and are then subject to municipal waste collection and treatment)
•
feces are cleaned up from the street by local cleaning departments (both with normal municipal
waste collection trucks and special small cars for collecting feces and dirt)
•feces are not cleaned up, i.e., they represent a direct emission to the environment.
It was assumed that a certain share of feces was picked up by the dog owners and disposed of
either in public bins on the street or at home (on average 15% in Berlin, Germany). This waste is then
picked up by the municipal waste cleaning on their normal routes. Further, it was assumed, that half
of the remaining share of the feces, which are left on the streets (i.e., in our example of Berlin, 42.5%
of the total amount of feces) are picked up by special feces
´
collection cars by the municipal waste
cleaning, while the other half stays in the street/park and decomposes there.
An overview of the inventory data, data sources, and assumptions made are presented in Table 2.
The assumptions made for the collection of feces was done based on the estimations for the city of
Berlin in Germany and were tested in a scenario analysis (see Section 2.2.3).
2.2.3. Scenarios
Naturally, smaller or taller dogs, respectively lighter or heavier dogs, require less or more pet
food and also produce different amounts of excrements. Moreover, other factors like the age of the
dog, the activity level, the state of the health, and others can influence the amount of pet food required
and the amount of excrements produced by the dog. Therefore, the influence of both the amount of
pet food and excrements (i.e., parameters related to the dog
´
s weight) on the overall environmental
impacts was analyzed in a scenario analysis. For this study, we only considered different weights of a
dog to estimate the related different amount of pet food consumed and feces produced. We selected
two scenarios: A 7.5 kg dog and a 30 kg dog to represent a small and a big dog. Moreover, we analyzed
how the LCIA results changed depending on different life expectancies of a dog and chose 8 years and
18 years as examples to represent a dog with a rather low and a dog with a rather high life expectancy.
The pick-up-rate of the feces varies depending on the structure of the region (rural or urban), city,
country, age of the owner, and his/her behavior, etc. Therefore, the environmental impacts related to
different pick-up rates of the feces (i.e., parameter related to the EoL of excrements) were examined.
For the analysis of the two extremes, i.e., that 1) either all of the feces (100%) produced by a dog are
picked up in plastics bags by the dog
´
s owners and disposed to municipal waste bins or that 2) no
feces (0%) are picked up in plastic bags. Hence, the key differences between the two scenarios are:
•
100% pick-up scenario: Need for plastic bags, collection of bags by municipal cleaning company
with normal collection trucks during their normal routes, no use of special small cars.
•
0% pick-up scenario: No plastic bags, use of special small cars to collect a share of the feces
from the streets (here: 50% of the total amount), the remaining share enters the environment as a
direct emission.
The scenarios considered, the data used, and the data sources are summarized in Table 3.
Sustainability 2020,12, 3394 6 of 13
Table 2.
Inventory data (presented for an average dog of 15 kg with a life expectancy of 13 years) and
data sources.
Parameters Unit Inventory Data Sources
Excrements
Average amount of urine
l/day
l/lifetime
0.4
1898
Average results from experiments
by [18] (only mature dogs were
considered)
Amount of feces kg/day
kg/lifetime
0.2
949
Rounded average weight of feces
from three dogs on five days [18]
Feces are picked up and disposed of in plastic bags
Average number of bags
used
bags/day
bags/lifetime
21
9490
Average times of defecations per
day (based on the habits of the three
dogs supplying the samples for
these measurements)
Weight of one plastic bag
(Polyethylene Film
(PE-HD) without
additives)
g 20
Measuring the weight of a random
plastic bag picked up in a
‘dog-station’ in Berlin2
Average pick-up rate % 153
Estimation of an expert from the
municipal cleaning company in
Berlin, Germany [21]
Municipal waste collection and treatment
Truck, municipal waste
collection km 30 Estimated distance to landfill or
incineration based on [12]
Small cars operating on
the street to collect feces
and dirt
m/dog dirt 12
In total, the cars drive
approximately 20 km per day and
collect around 500 kg feces.
Assuming that one dog dirt weighs
around 0.3 kg, the car has to stop
(on average) every 12 m to collect
one dog dirt (calculation based on
experts’ opinion from [21])
Waste to municipal
waste incineration % 55 Estimation based on data supplied
by [22] (the same estimation was
made in [12])
Waste to landfill % 45
Note
1
Two bags are needed when it is assumed that all feces (i.e., 100%) are picked up. This number is used in
this model, even though the pick-up rate was calculated with 15%, which would require less bags. However, it is
used here as a conservative approach.
2
A ‘dog-station
´
is a public bin and a deposit of bags to pick up and dispose
the dog feces.
3
According to expert’s opinion the pick-up rate in Berlin is 15% and one of the lowest in big cities
in Germany.
Table 3.
Scenario analysis: Parameters related to the dog (size and lifetime) and the EoL of excrements
(pick-up rate), as well as data sources and assumptions.
Parameters Unit Average
Dog Scenarios Data Sources and Assumptions
Lifetime Year 13 8 18
It is assumed that the life expectancy of dogs varies
on average between 8 and 18 years (using data from
[13,14])
Weight Kg 15 7.5 30
It is assumed that an average small dog weighs
around 8 kg and an average big dog around 30 kg
(based on data from, e.g., [23]). For this study, the
numbers 7.5 kg and 30 kg are chosen, which
represent dogs weighing half as much and twice as
much as the average dog.
Pet food
(average
amount)
kg/lifetime 4528 1588 6563
The pet food per weight is calculated as followed 110
[kcal] *dog weight 0.75[kg] (Based on [12])
Feces (average
amount) g/lifetime 949 584 1314 The amount of feces and urine produced over
different lifetimes is calculated based on the data for
the average dog, assuming a linear relation.
Urine (average
amount) l/lifetime 1898 1168 2628
Pick up rate % 15 100 0
Here, the two extremes are considered, i.e., that no
feces or all feces are picked up in plastic bags by the
dog owners.
Sustainability 2020,12, 3394 7 of 13
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%.
Table 4. LCIA results for an average dog (15 kg, life expectancy of 13 years and a pickup-rate of feces
of 15%), absolute values.
Impact Category (Expressed as Potential) Unit LCIA Results
Climate change kg CO2eq 8.2 ×103
Ozone depletion kg CFC-11 eq 7.9 ×10−4
Human toxicity, cancer CTUh 3.6 ×10−4
Human toxicity, non-cancer CTUh 2.5 ×10−3
Particulate matter kg PM2.5 eq 3.5
Ionizing radiation (human health effects) kBq U235 eq 480
Photochemical ozone formation kg NMVOC eq 25
Acidification molc H+eq 64
Terrestrial eutrophication molc N eq 220
Freshwater eutrophication kg P eq 5.0
Marine eutrophication kg N eq 21
Freshwater ecotoxicity CTUe 1.8 ×104
Land use kg C deficit 7.4 ×104
Water depletion m3water eq 34
Resource depletion (mineral, fossil, renewable) kg Sb eq 1.6
To evaluate the results shown in Table 4and 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 CO
2
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 CO
2
eq, which equals around 7% of the annual greenhouse gas (GHG)
emissions of an average German citizen (in 2016 around 11.1 tons CO
2
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 CO2eq. 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.
Sustainability 2020,12, 3394 8 of 13
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.
Sustainability2020,12,xFORPEERREVIEW8of14
causedbytreating6.5haarablelandforoneyearwiththeherbicideglyphosate(accordingto[27]
around2.8kgofglyphosateareusedperhaperyear,whichequalsafreshwaterecotoxicitypotential
ofaround1500CTUe)
.
Thetotalfreshwatereutrophicationpotentialofadogisaround5.0kgPeq.,
which would equal the eutrophication potential caused by producing 21900 l of beer [28]. These
examplesobviouslydonotintendanycomparisonbetweentheseratherdifferentproducts,theyjust
servethepurposeofprovidingareferenceforanunderstandingoftheordersofmagnitudeofthe
impactsofadog.
3.2.RelativeContributionofLifeCycleStages
Thecontributionofthedifferentlifecyclestages/processeswithintheproductsystemofadog
to the total result is displayed in Figure 2. Except for the impact categories of freshwater
eutrophicationpotentialandfreshwaterecotoxicitypotential,themaincontributiontoalltheimpact
categoriescomesfromthelifecyclestagepetfood.Here,theimpactinmostcategoriesismainly
causedbytheprocesses´ingredients´and´packagingproduction’[12].Thecategoryoffreshwater
eutrophicationismainlydeterminedbythedog´surine(around44%)andthedog´sfeces(around
43%).Thisismainlycausedbyphosphorouscontainedintheexcrements.Urinedoesnotcontribute
significantlytoanyothercategory,whilefeceshaveasignificantcontribution(around50%)alsoto
thecategoryoffreshwaterecotoxicitypotential.Impactsrelatedtotheplasticbagproductionare
visible in the category of water depletion potential (around 9%). Impacts related to the waste
collectionsteparenotvisibleinseveralcategoriesbutneverexceed5%.Relevantcontributionsofthe
EoLstage,which,inFigure2,includetheincinerationandlandfillofmunicipalwaste,canbeseen
onlyforthecategoryofclimatechangepotential(around7%).Thenegativevaluesintheimpactcategorywaterdepletionresultfromcredits
providedforwastetreatment/incinerationintheEoLstageduetoenergyrecovery.
Figure2.Relativecontributiontoimpactcategoriesbylifecyclestages/processesforanaveragedog
(15kg,lifeexpectancyof13years)andanaveragepick‐up‐rateof15%.
3.3.NormalizedLCIAResults
NormalizationisanoptionalstepofLCIA,whichallowsthepractitionertoexpresstheresults
usingacommonreferencevalue[29].Forthisstudy,wechosetheEuropeandomesticmarketasa
referenceimpactandusedthenormalizationfactors(NF)providedbytheEuropeanCommission
(EC)inthecontextoftheEuropeanEnvironmentalFootprint[30].Normalizationfactorsexpressthe
Figure 2.
Relative contribution to impact categories by life cycle stages/processes for an average dog
(15 kg, life expectancy of 13 years) and an average pick-up-rate of 15%.
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
Sustainability 2020,12, 3394 9 of 13
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 3shows 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 3are 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).
1
Figure3.LCIAresultsofanaveragedog(15kg,lifeexpectancyof13years)andanaveragepick‐up‐
rateof15%normalizedtothetotalimpactsoccurringintheEUdomesticmarketperpersonperyear.
3.Kasielke,T.;Buch,C.UrbaneBödenimRuhrgebiet.InOnline‐VeröffentlichungendesBochumerBotanischen
Vereins;Bochum:2011;Volume3.Availableonline:https://www.botanik‐
bochum.de/publ/OVBBV3_7_Kasielke_Buch_UrbaneBoedenRuhrgebiet.pdf(accessedon11April2020)
Figure 3.
LCIA results of an average dog (15 kg, life expectancy of 13 years) and an average pick-up-rate
of 15% normalized to the total impacts occurring in the EU domestic market per person per year.
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 4correspond 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
Table 5shows 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
Sustainability 2020,12, 3394 10 of 13
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.
Table 5.
LCIA results of the scenario analyses: Variation of the age and the weight of a dog (assuming
a 15% pick-up rate of feces), absolute values.
Impact Categories (Expressed as Potential) Unit
Small Dog with Low
Life Expectancy
(7.5 kg, 8 years)
Big Dog with High
Life Expectancy
(30 kg, 18 years)
Climate change kg CO2eq 3.0 ×1031.9 ×104
Ozone depletion kg CFC-11 eq 2.9 ×10−41.8 ×10−3
Human toxicity, cancer CTUh 1.3 ×10−48.4 ×10−4
Human toxicity, non-cancer CTUh 9.0 ×10−45.8 ×10−3
Particulate matter kg PM2.5 eq 1.3 8.1
Ionizing radiation (human health effects) kBq U235 eq 180 1.1 ×103
Photochemical ozone formation kg NMVOC eq 9.2 58
Acidification molc H+eq 23 150
Terrestrial eutrophication molc N eq 81 510
Freshwater eutrophication kg P eq 1.8 12
Marine eutrophication kg N eq 7.6 48
Freshwater ecotoxicity CTUe 6.6 ×1034.2 ×104
Land use kg C deficit 2.7 ×1041.7 ×105
Water depletion m3water eq 12 79
Resource depletion (mineral, fossil, renewable)
kg Sb eq 0.58 3.7
Compared to the impacts of the average 15 kg dog caused during its 13-year lifetime (e.g., 8200 kg
CO
2
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 CO
2
eq.) while the impacts caused by a big 30 kg dog that lives 18 years, would be more
than twice as high (e.g., 19000 kg CO2eq.).
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.
Sustainability 2020,12, 3394 11 of 13
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
,
32
], 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
–
36
]), 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.
•Regional differences
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.
Supplementary Materials:
The following are available online at http://www.mdpi.com/2071-1050/12/8/3394/s1,
Figure S1: LCIA results for an average dog (15 kg, life expectancy of 13 years) and an average pick-up-rate of 15%
normalized to the total impacts occurring in the EU domestic market per person per year, Table S1: Composition
of the excrements of a dog (feces and urine). The results for “feces to soil” are average values based on three
samples (each from a different dog), analyzed by Raiffeisen Laborservice
1
. The results for “urine to soil” are
average values based on the urine collected from 3 dogs on 5 days by Schaepe 20112.
Sustainability 2020,12, 3394 12 of 13
Author Contributions:
Conceptualization, M.F.; methodology, M.F. and A.L.; investigation, K.M.Y. and A.L.;
data curation, K.M.Y.; writing—original draft preparation, K.M.Y.; writing—review and editing, A.L. and M.F.;
supervision, M.F.; project administration, A.L. All authors have read and agreed to the published version of
the manuscript.
Funding: This research received no external funding.
Acknowledgments:
We acknowledge support by the German Research Foundation and the Open Access
Publication Fund of TU Berlin.
Conflicts of Interest: The authors declare no conflict of interest.
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